I'm just thinking out loud really, I'll be making very few mods to the car, mostly geo, but I insist the brakes are right on anything I own. We have a lot of OEM cross over in the VAG world and most stuff fits in some way, shape or form for cheap, effective upgrades.
I wasn't so much thinking of changing the caliper, more using the RS250's carrier and 340mm disc. It doesn't surprise me the caliper is different, I'd imagine they've selected larger piston sizes but it may still share the same body and pad family? The Clio uses the code Brembo HP 4 PISTON 125X65 Pagid p/no. 8023. Can anyone find out if the RS250 shares this? (Image below) It'll give an idea on compatibility. Maybe compare the Renault parts system, as the aftermarket hasn't caught up yet.
I've found the Clio's disc is 63mm high, so I need to see if the RS250's is the same? If it is, then it is very easy to engineer a caliper outboard, changing its offset however is a PITA. The other issue is the Brembo caliper is a bulky bugger, so getting it behind a 17 may be a problem.
If I ruin the discs, then I'll almost certainly go down the 2-piece route with ducting for the weight saving alone. But there's no harm in finding out if the RS250's will work for other people's benefit.