What PSU are you using even? Apparently the 5830 will be out in Feb - should be between 5770 and 5850, although 5770 with its 800 shaders and 1GB of GDDR5 will be quite a bit faster than your 112 shader, 512MB GDDR3 9800 GT. If you check our 5670 review recently we included the 5750 in that which quite comfortably beat the 9800 GT at low-medium resolutions: http://www.bit-tech.net/hardware/graphics/2010/01/14/ati-radeon-hd-5670-review/4 aaand then if you see the 5750 review, the 5770 is again faster.. http://www.bit-tech.net/hardware/graphics/2009/11/06/sapphire-ati-radeon-hd-5750-1gb-review/3 But I'd say for what you want $200 won't cut it, plus you'll likely be CPU bottlenecked at just 2.3GHz on your Q8200.
Sounds like just about everything needs to change if you want your better performance to have measurable reliability...! I'd spend some of the $200 on a Corsair modular around 500W, and a new cooler that comes with a 1156-compatible 'plate. That way your rather under-exercised Q8200 will be able to stretch it's legs so as not to choke the new GPU, and you won't lose money buying components you can't switch into the 1156 build the future almost certainly holds.
if your looking for a big increase on your gpu why not a 4890? pros - you can pick them up cheap now, still get a 300 case and decent psu cons - could be noisy (depending on maker) and is not dx11 if your set on 5### series
So, 922 at $100. http://www.newegg.com/Product/Product.aspx?Item=N82E16811119197 and a Corsair 650 watt at $100. http://www.newegg.com/Product/Product.aspx?Item=N82E16817139005 There wouldn't happen to be any cheaper PSUs in that range/quality? [I'm set on the case.]
A Corsair 550VX at $80 may work for you. The problem is that you have yet to decide what you want it to work with. For example an overclocked i5 750 and a Radeon 5850 should be fine with a 550W PSU however if you ended up with an overclocked i7 920 and a Fermi graphics card the extra 100W may come in very handy. I would suggest sticking with the 650TX, particularly as Newegg seem to have knocked the price down to $90. Some comparable units are Seasonic or Enermax