That really depends on the CPU, RAM, Power Supply and motherboard you are using. In most cases, 3.2Ghz CPUs will hit 3.6Ghz with a excellent XP-90 or XP-120 heatsink from Thermalright coupled with a Panaflo fan.
Thats the exact setup I used to have. 3.6 is no problem. In fact, my WC system hits that no problem. I always seem to run into problems afterwards when I get up to 3.75, even though thats not a very significant overclock.