unless you have very large differences in temp (phase change/air for example) you wont get anything. The only advantage from a performance perspective is that you wont fry your chip when you vmod them...
Thats ofcourse assuming your comparing your chips real limit, with its new limit. If you had it o/c too much before and it was slightly overheated, making it unstable but you thought it was stable, then extra cooling will give you that much...
ok i lied. 10c will give you about 10-20mhz. I wouldnt say thats worth noting...