60ÂºC is your load temp on the i5-750, right? doesn't seem too bad considering you are using the stock cooler...If you can afford to buy an aftermarket cooler, the CM Hyper 212+ has good reviews and performs well for its price.it would shave some 10ÂºC on those temps at the least.
Either go with a H50/70 or one of those monster Noctua NH-D14 for an extreme OC, they are very good. I don't have much info on the Corsair H50, but i think you can adjust the fan speed. For better performance you should run it at max speed
You haven't stated what MSI board you have/will buy, so i can't say it will be possible for you to save OC profiles.It depends on the BIOS of the board, or if it sports a OC app that you can use in windows and OC from there.
With the Q6600 you should be able to easily get to 3.6GHz ( 400*9) at 1.4-1.45V. For reaching this mark without having to OC your RAM you should use a 800MHz or higher speed kit, and set the RAM multiplier to 1:1.
The more airflow you get on the case the better. The Antec 300 is a fine case, but if you want to switch it to the 900 is up to you