i have a cinq sporting and my mate (gex) has a sei sporting. However his is a 1242 abarth. His car looks nicer than mine and obviously having a bigger engine is faster. I think my cinq handles better tho as his feels like quite a bit bigger of a car than it really is. I don't like the sei dashboard one bit.. the centre console is nicer than the cinqs.. but why did they attach a tacky carbon fibre look.. when driving the sei, i can't see any of the warning/dash lights because the steering wheel obscures them all!
tbh, unless your cinq was in bad condition and needed serious cash spent on it, i wouldnt bother making the switch. They're both great cars with good points, and bad points.