Hey, here is what I am thinking.
If you want to get to 3.5ghz, you'd need 7x500 or PC8000 ram. If your current ram cannot do PC8000, it will become unusable. Which means in the best case scenario you will get roughly 17% performance increase of going from 3.01 to 3.5ghz C2D and will have 2 gigs of ram.
Of course there are also no guarantees that your cpu will clock to 3.5ghz.
However, it's not as if 3.0ghz C2D is bottlenecking your system. By the time it will, 8800GTS 320 will be far more limiting for gaming. So instead of spending $180 on 2 gigs and throwing away 1 gig, you could just get 1 extra stick for $50 and pocket $130 towards your next big upgrade (like the graphics card). Think of it as $ put aside for a rainy day. At the same time going to 2gb will provide for a smoother gaming experience and faster loading times (somewhat), while not breaking the bank.
In my opinion, by the time you'll feel that 3.0ghz is too slow, you'll probably be looking to buy and overclock a cheap Quad-core anyway.
I myself have this
Corsair 5400 2gb kit $70. I got it in October for $200 and it's revision 7.1 with ProMos chip. It does
1000mhz making it a smoking value. However, you probably cant guarantee same revision and the chips might not overclock that well.
I say you just get 1 extra stick DDR2 800 for as cheap as possible to match your 430mhz overclock and save your $ for a more substantial upgrade.
Also take a look at
This
Under high resolutions (which is what top end cards are used at), there is no noticeable performance benefit today from C2D at 4.2ghz vs. 2.66ghz with a 8800GTX, nevermind 8800GTS 320mb. This should make you reconsider the importance of going from 3.0 to 3.5ghz.