I think I'd go with a CPU cooler and keep the i5-750 instead of going with the i5-760. A good option for some overclock action. Sunbeam 120 mm Core-Contact Freezer CPU Cooler $40
and $15 rebate. +$25
Upgrade the PSU to handle a possible future 2nd HD 5770 or a larger single video. Antec NEO ECO 520C 520W $50
and $20 rebate + $0
--> note: limited time offer on this PSU. It's a 40amp +12v rated PSU, a jump up from 30amp of the Corsair 400CX.
And a case upgrade: Antec Three Hundred Illusion $70
After adding things up it's looking like that $15 difference between i5-750 and 760 can fit into your $100 upgrade. Your choice.