I've just come from a 245hp Mk4 Ibiza Cupra with a 1.8 20vt to a mk4 r32, fuel difference isnt too bad, a tank costs £20 more but i get about 30-50 more miles out the tank (i've been advised i dont drive the r32 properly though haha)
Main difference for me is the grip from the r32, the independant rear suspension must really help and of course the haldex when you're pushing it, the noise is amazing too and the interior of course! The cupra was abit lairy to drive, even with a fancy diff, r32 is allot more relaxed and has calmed me down allot. I think this is because it needs to be revved to go fast whereas there was that much torque low down with the cupra, it kind of got abit addictive!
Only petrol mk4 i'd go for would be the r32, i'd much rather a Leon Cupra R other-wise.