I am using 17" TSW wheels with 215/45 tyres.
Speedo is right compared with a GPS gadget.
Maximum 5% error at low speed.
Same here. 215/45 r17 is in the end 2-3% bigger wheel combo, and offsets the stock small underreading of the speedo (compared to gps).
I've found that ride improved significantly when i switched from stock 225/45 r16 to non-factory size.
Could be the slightly bigger wheel, lighter 17" alloys (-2kg compared to 16" 20vT Plus double spokes), and fresh tires with softer sidewall.
The bigger wheel scrubbed the front arch lining on full lock when I had new Goodyear Excellence tires, it stopped when they wore out. It didn't scrub when i fitted new Uniroyal Rainsport3.
I wrote all this because You wanted to fit higher profile tires = bigger wheel diameter combo. In my oppinion, 215/45 r17 is on the limit (scrubbing), so anything bigger will most likely cause issues. Keep in mind, not all tires of the nominally same dimensions (eg. 215/45) are exactly the same.