I believe the chances are pretty good that the 555 would unlock, that being said, it is somewhat of a gamble. Heat will not be an issue because the PC will be setup like a standard rig, located in my home office. I will stream content from it to my ps3 hooked up to my 1080 TV. I assume that in recommending the 620/630, you are saying that the i5 is overblown or in other words, it will not do a better job, just be faster at similar tasks.