E5200 want to upgrade for gaming mostly but keep the mobo. Gigabyte p35 DSL3
I doubt you can get the Extreme processors for a reasonable amount. So your next best bets are:
Q9650, Q9550, Q6700 and Q6600 G0 (in that order of preference). Your board
supports all of those without problems.
DS3L craps out at 425 FSB or so on Quads (I had mine at 430 or so but that required too high of a FSB termination voltage for 45nm Quads; and I replaced the Northbridge thermal paste

). So basically you'll want a Quad with the highest multiplier you can get.
Q9650 = 9.0 Multi x 425 = 3.8ghz
Q9550 = 8.5 Multi x 425 = 3.6ghz
Q6700 = 9.5 Multi x 425 = 4.0ghz (not happening on air) - but means you can max out this CPU easily
Q6600 = 9 Multi x 425 = 3.8ghz (not happening on air) - but means you can max out this CPU easily
Although a more reasonable 24/7 operation for the DS3L is around 400-410 FSB (you may be able to pull off 410 FSB without raising the MCH or FSB voltage by more than +0.1V). I believe the FSB Termination voltage on the DS3L at stock is 1.3V, so adding +0.2V will take you way over the safe 1.45V limit for 45nm quads. So ideally, you will want to keep your FSB voltage at 1.4V or below (so this is why 410-415 FSB is prob max for 45nm quads and 425 FSB for 65nm quads).
The board also has weak power circuitry. So since yours isn't new anymore, you may not necessarily crack more than 425FSB overclock. Although, I can attest that I ran my Q6600 3.4ghz @ 378 FSB loaded 24/7 crunching for 2 straight years. So I know the little board can take a beating with the latest BIOS in hand.
Just make sure you get a good aftermarket cooler as Q6600/6700 series run especially hot. If you can find a used Q6600/6700 for $80 or so, that's a very cheap upgrade to hold you over until next year. Obviously the Q9550/Q9650 would be the best option, but those might run more expensive due to higher demand and the fact that they were more high end to begin with.