Don't do it KC. It will do one of two things, you will either be completely consumed by it ,and itll be all you ever think about for a good 6 months. Which is what happened to me with GT4....
OR, you will realise that the nigh on 1 hour it takes too install all the important gubbins from GT5 onto your PS3's HDD just isn't worth it and after 2 hours playing it, think it's just not a patch on GT4.
Which is how I felt.