I want to get a custom PC built, but need help choosing the processor. I was looking at quad core processors, shall I go for the Q6700 @ 2.66GHz or Q9450 @ 2.66Ghz which is a bit more, but with a higher FSB and cache. Or is there more better recommendation. I will be using the PC for mostly playing games minor work use. Any help appreciated.

How much more are you talking about?  It's little better performing, but I wouldn't pay too much more for it.  I'd say stick with the Q6700 unless it is only a few bucks more for the Q9450.  But do give specific prices if possible, please.

 About $100 more. Deff not worth ti stick wiht Q6700 espcially since I think that Q450 is being repalced but Id have to double check.

The Q9450 is £44 which is probably about $90, more then the Q6700.

How much of a difference in performance will the Q9450 make compared to the Q6700?

Get the Q6700 then.  It really doesn't perform faster.  For gaming, it's virtually the same performance.

 Good idea