I've experienced the same problem most of people have: gt5 hangs on silver logo. I searched the forum, but there's not an unique solution for that.
I've tried lots of payloads, some of them gt5 works, some don't. So I think the problem for those that can't run gt5 is on the payload they are using. But the problem is that having the most update payload for your dongle does not means that the game will run normally.
I have p3hub2 and psbreak 1.2, but have tested only p3hub2. For this dongle the most update payload (Hermes with 3.55 spoof) hangs on silver logo. I used the same hex but with an older version of payload 1.7 and it does not work.
So I got the older hex with the original 1.7 and it worked just fine. I don't know if this problem is exclusive to p3hub2 or all dongles can have the same problem, so later I'll try ps3break 1.2 and see which payloads are working. But my tip for those who are stuck on silver logo is to try out different payloads so one of them should work.