ran off some figures from my "ever developing model"....for 6000rpm....

pred. shaft hp__ density kg/m3 ____pulley & cool setup _______________Fuel lb/hr/injector___intake cfm ______rpm
350___________2.08 _________74/155 stock 14.5psi 9kW cool 122F AIT _______42____________640 _______6000_____STOCK
+29__________ 2.25 _________65/155 18.5psi stock9kW Cool 154F AIT________46____________694 _______3500____COMFORTABLE
+50__________ 2.38 _________65/155 18.5psi stock9+8kWCool 122F AIT _____48____________733________ 6000____SWEET
+77__________ 2.54 _________65/185 25psi Stock9Cool 194F AIT ___________52____________783 ________2000____COOKED!
+130_________ 2.85__________65/185 25psi 9+22kW Cool 122F AIT _________58____________879 _______6000_____CRAZY!!!!

All seems to make sense - even at 18.5psi you gotta get a whole lotta cooling if you are running over 3500rpm consistently.....might be hard to achieve tho....so you could risk a 65mm without too much concern unless you're hill climbing or something
PS - I'm assuming stock AIT at 6000rpm is 122F and the stock IC+circuit is pulling about 9-10kW out of the system.
the rpm is the "averaged" figure you could run before the stock cooler begins to get overloaded and AIT's climb.
It may be that the stock cooler will be overloaded at 6000rpm to begin with. Ive assumed it isnt though - still working on reality checks on this.
It also assumes a constant eff. on the SC of 65%....need to work on that, 'cause I know it drops off above 20psi
PS - 12.8 AFR

These might raise a conversation - but hey - lets have it....!