Bit of a late reply, but I do have an SSD in my PS3, I know the PS3 is only Sata II compatible, but I have installed a 60gb SSD 3, which I had laying around spare.
For GT5, the only game I actually play - it is awesome.
I have the signature edition, as I am a big fan. To do the initial GT5 install it took around 3 minutes. I then ran all the updates, the updates took a while to download, but it installed them in literally seconds.
I have NEVER waited more than 5 seconds for a race to load and be ready to go, since the upgrade.
Luckily I have never claimed my chromeline or stealth cars, so starting fresh wasnt such a bad thing!
(on a side note, I did notice DLC codes expire 31/Dec/2011)