I currently run a decat but I'm thinking of getting some kind of low-restriction cat fitted instead. I know there would be some loss of performance, but would the car run ok without remapping if I were to fit a cat? The car's currently in quite a high state of tune - around 400bhp.

Thanks,
Dan

Even a sports cat will cause quite a fair amount of restriction (and some loss of horsepower) on a turbicharged car. So you should definitely get it on the dyno to check how it runs at high load. Boost, AFR and det need to be monitored

be carefull with proper sizing of cat !

there should be BHP ceiling recomendation, from core manufaturer ... eg. 100mm diameter, 200CPSI core sport cat is suitable for 150-170bhp max, othervise serious increase of backpressure will occur, (as I had on my 2l 16v NA with 100mm dia/200cpsi universal sports cat and was able to rev up to 3500rpm/WOT without problems..., but turbo engines are not so sensitive to that.. ther will be only some lost of power...)

this backpressure could cause engine running slightly leaner...

so for 400bhp u need at least twice area of core, or smaller density... so at least 130mm+ core/100cpsi should be good for small amount of backpressure