OK so still not bought my bike, but am getting close now, but have a query on geometry and sizes.

I had chosen to purchase the Cannondale CAADX Tiagra HERE

However, I happened to have a quick squizz on Planet X today and saw this HERE

Its better brakes, better gears, better wheels, better bike, for the same money and they will accept the "cycle to work" scheme.

The main issue is, I can't try the PlanetX prior to purchase, which is a worry. With the Cannondale the 58 was a perfect fit, and looking at the PlanetX the 59 would seem to be more like for like with the 58.

My problem is with long arms and longish legs, I have tried most bikes, and they feel too cramped, so I guess I need a long top tube, with a reasonable reach.

So what do people think, I can return the PlanetX if need be, but I am sure it will be hassle, but should I go for a plunge in the dark or be safe and purchase a slightly inferior bike but one I know will fit..

Thanks y'all for your thoughts..

So long as it's broadly right, you can always adapt it to fit you better: shift the saddle backwards and forwards and adjust the stem length. With a 58 or 59 frame, I'm guessing you're 6'1"- 6'2"
I'm 6' with a 33" inside leg and typically ride a 56-57

Look for the "effective top tube" length for both and see that they're pretty much the same.

And I am guessing you'd say the planetX over the Caadx MRS?

Other question, do PlanetX ever have a sale?

Yes - I'm the world's biggest fab of disc brakes. Throw in 105 rather than a Tiagra and I'm sold.

Yes - worth asking them when the next one is.

The planetx is 105 with BB7s, for under a grand I cn't see I can do better!

Hard to. What's the Boardman CX these days?

BB5s with SRAM, so not quite as good and the internet seems to say the BB5 are quite inferior to the 7s, and most people seem to look to upgrade back to BB7.

Both bikes have quite a narrow range of gears, both 36-46 up front and 12-28 on the CAADX and slightly better 11-28 on the Planet-X. On my commute up some short steep sections I found I needed the "granny wheel" effect of a larger rear cassette (ie: going up to 28 or 32, with smaller front wheel 34) and a larger front wheel (50-34 is common on many bikes) for a higher top speed (or the same speed without your legs falling off at a massive cadence).

But it depends on where you will be riding and how fast you want to go. Neither of them have mudguard eyes / rack mounts for example...

As for sizing, the Caadx "58" is 57cm b/b to top of seat tube, the same as the Planet-X 57 (I think, the Planet-X geometry page is confusing) but you think a Planet-X 59 would be better? Might be worth getting Planet-X to send you some more detailed geometry info.

Like you JimO, I tend to prefer over-large frames, I have a Boardman CX Team medium when really I should have a small, but as MRS says you can move the saddle back and get a longer stem, although (as with the gears) it's nice for it to be just right straight out of the box, and that includes a good set of tyres. The Planet-X pics show CX Pro tyres but the specs say something else?

The internal cable runs along the top tube of the Planet-X looks better IMHO than the external Caadx cables, and the 105 groupset is theoretically better than Tiagra.

Planet-X would do it for me...although being all black it's a bit dull to look at...

Yup, but as Dave says, it does at least have mudguard (and rack) eyes. I swapped the front caliper on mine for BB7. I also swapped the SRAM for 105 (sold the SRAM for as much as I paid for the 105). But not everyone wants to go to that bother. Also paid well under £1000 (£800 ish) with various discounts available.

The Planet-X looks fine though

Like MRS, I upgraded the BB5's on the Boardman to BB7's, but kept the SRAM groupset. It's quite a clunky gear change compared to 105 IMHO, and at the moment I have a lot of trouble changing up from 34 to 50 at the front, with it either not catching at all, or the chain falling off, probably needs adjusting by an "expert". Also the OE tyres on the Boardman were paper thin and I had loads of punctures until I changed tyres. Despite having just sold two other CX bikes (Giant and Specialized) I have kept the Boardman, heavy as it is, because it's a good go-anywhere bike. They come up often in eBay too, there's a rather used one from Dorking up at the moment...

Note PX add 10-12.5% to the cost if using C2W depending on the scheme

http://www.planetx.co.uk/cycle-scheme

I don't know how that works if your C2W limit is 1k and the bike is 1k as then it would be £1100

Thanks Vicks, I saw that. Will have to do some sums to see what makes better financial sense. My C2W is capped at 1k, but I can go over and pay the difference.

I rang PX on friday and am waiting a call back on best price and a few other bits of info..

Have Fudges got the C'dale for a ride?

All I will say is that black bikes are boring

Fudges had the Cdale at a rock bottom price and I stupidly had a baby and missed out on it - my fault I guess!

I quite like the black look, very stealth - not sure it will still be stealth with me atop though

Not getting the cheap Cdale is possibly a blessing?

The carbon frame on the PlanetX would be the biggest draw for me.

Having run 105 and Tiagra I've found the 105 chain / cassette combo have a lot more miles in them.

I'm also a disc fan, although the drawbacks seem to be that they eat bearings (perhaps putting the stopping force through the bearings kills them?), and they work much better with OE pads.
On the positive side the power / control in all conditions and the awfulness (IMO) of cantilever brakes makes it an easy choice.

There are some interesting carbon rimmed 700c disc wheels from China claiming 1390 g weight for the pair on eBay currently. A friend has some similar wheels and they are unbelievably easy to spin up.

Imagining you take 8-900g out of the bike that way you're probably getting towards a machine that will hang on to most road bikes.