Matching memory - how much of a performance difference?

[iqwertyi]

Hello.

I've got a friend who just got a Dell which comes with 2 512 sticks.
They'd like to upgrade to 4 gigs eventually.
So, how much of a performance difference would it be to get ONE 2 Gig stick now and pair it with one of the 512.

vs.

Just putting one 2 gig in one bank.

vs.

2-1 Gig (not really ideal for them since they eventually want to go 4 gigs)

Just looking at performance hits.
They don't game much at all.
mostly photoshop and Office.

Thanks.

 

[-=Antimatter=-]

Buy 4GB now, it will be under $100 and prices aren't going anywhere but up in the next 6 months.