first of all, since your budget is nearer to 50k, dont bother to stretch another ~10k for Gen2 CPS... too much... unless u got a lot of extra money and willing (and capable) to stretch your budget after all...

as for the IAFM and CPS difference, IAFM is Campro basic + new intake module fixing the torque dip... that's all... while CPS it got variable valve lift boosting the performance another 15hp...

problems, engine wise (CPS, i dont know IAFM) so far no problem with mine though it only aged 1year and 4 month... other parts problem... a few, but nothing serious... the worse is the splash shield issue at high speed... Performance, more than what I expected from a Proton especially the handling... 

FC wise, since my right foot is pretty much welded to the floor, people will see my car's FC is off the roof. but at one time of my test, CPS with RON97 Primax3 manage to get 5.5L/100km on 100% highway maintained at ~3100RPM @ 110km/h with cruise control... the worst could be 20sen/km (old pricing of RON95 @ RM1.80/L)

I dont drive IAFM so I dont know anything about it other than a little bit technical stuff.