The IA isn't UCI legal but it's a lot more adjustable than the Scott, so you need to pick which is your priority.
Plasma 5 unchanged and will still be around for MY19 at least

The main differentiator is fit. Most of the superbikes are very limited on this front, so the performance differences show up in not being able to get the rider into the best position.
Same on aero depends on your definition of 'same' - most testing shows a 30-60s advantage over IM for a P5 vs anything other than the SCII.