Not sure what happened to the original post, so here's an updated version.
Current specs for my stock HP Pavilion m9451uk:
IPIBL-LB (Benicia) Motherboard
Intel Q8200 @ 2.33GHz
4GB DDR2 RAM @ 800MHz
Nvidia Geforce 9600GS
Bestec 300W PSU
Max Resolution 1600x1200
Would like high or better graphic settings for games like Crysis 2, Civ 5, DOW2 and Crysis/Farcry 3 when they come out.
The short question first:
My current card seemed to be doing alright up until the fan bearings went and the cheap replacement I bought can't keep the temperature down while gaming. Would simply buying a decent new fan/heatsink and working out how to overclock the card give me reasonable graphics? I also noticed that other 9600 cards (GT, GSO) need a 6-pin power connector which mine doesn't have, is this likely to be relevant?
And the long one:
When I started looking for a new graphics card for my current 300W PSU I quickly realised my choices were limited. I want GDDR5 RAM if I get a new card and after a bit of research I can find no cards that match both requirements. I've decided I'd need a new PSU as well, 500W or so should do as I'm not planning on any multi-screen powergaming (and I might be getting a 550W for free anyway), so I expanded my search to include 500W cards.
The best card as recommended most often on this and other forums for these new parameters is the HD6850 which I can get for £90. But another option presented repeatedly for a 300W supply was the HD6670, even though the specs say that it requires a 400W supply (same as my current 9600GS claims to need). So I had a look at other graphics cards that say they need 400W, the best I saw was the GeForce GTX 550 Ti.
I can get the GeForce for £85 (£90-95 for an overclocked one with a big fan), so I wonder if the GTX 550 Ti would also run on my 300W supply? What would happen if I tried it and my PSU wasn't up to the task? The overclocked ones would presumably draw more power so would people's advice be against trying it with them? I have looked at the equivalent AMD cards as compared on the tomshardware hierarchy and they all have higher recommended power requirements than the GeForce, so I'm largely ignoring them as I'd get the 6850 if I need a new PSU as well.
In short, if I can't get the free PSU, would the GeForce be a good budget alternative to avoid having to buy a new power supply as well?
Feel free to comment on anything else I've said as I'd hate to find I made a mistake after spending the cash.