I have a EU version of GT5, but I use a a US account.If I wanted to purchase a DLC on the US Store, could I then use it in the game, even though I have a EU disc?
You need a EU account set-up. I've done it so I could get all 6 Stealth models as well as the 6th Chrome Line Jag Race Car. BUT, you will need a 2nd PS3 as the account has to be a main one. Lucky for me, I had an old fatty kicking around.