2x9800 GT vs 1xGTX460 - Is this an upgrade?

[ReliantLion]

I'm looking to upgrade:

APPROXIMATE PURCHASE DATE: Within 2 months. Purchases staggered if getting 2 cheaper cards in SLI.
BUDGET RANGE: ~$400 (~$200x2) before rebates
USAGE FROM MOST TO LEAST IMPORTANT: Skyrim, MW3, etc.
CURRENT GPU: 2x 9800 GT in SLI.
POWER SUPPLY: Corsair 620W
CPU: Intel Core 2 Duo E8500 Wolfdale 3.16GHz
Mobo: ASUS P5N-D LGA 775 NVIDIA nForce 750i SLI ATX Intel Motherboard
PREFERRED WEBSITE(S) FOR PARTS: Newegg, Amazon
PARTS PREFERENCES: nVidia (my mobo uses SLI), ASUS, Gigabyte
OVERCLOCKING: No
SLI: Maybe
MONITOR RESOLUTION: 2048x1152

ADDITIONAL COMMENTS: What I really want to know, is how does my current config compare to if I got either 1 or 2 GTX 460's? I'm looking at ASUS ENGTX460 DC TOP/2DI/1GD5/V2 GeForce GTX 460 (Fermi).
I want to buy one of these now, to make sure it's compatible with my system, then in a month or two, buy another for SLI. I think it's worth mentioning I have a HAF case, so physical size is not an issue, nor is air flow.
SPECIFIC QUESTIONS I'D LIKE ANSWERED:
1) Will one be as good or better than the above?
2) Should I wait and get a $400 dollar card next month (no SLI)? I am aware if I did this, I could keep one of the 9800's as Physx, but not many games support.
3) What are power requirements these days? Would I need to upgrade my PSU? If so, this would need to fit into the same $400 budget.

 

[nforce4max]

Yes by about 20% overall especially when accounting for the overclocking room of the 460 however I own both and can tell you that the 460 isn't idiot proof unlike the old cards. It will use more power when you start pushing the 460 to 850-900mhz.

 

[ReliantLion]

Is the 20% for just one of these? Or 2 in SLI?

 

[pro-gamer]

of course gtx 460 is a regular use for gamming
1 gtx 460 is better than x2 9800gt becuase gtx460 have 336 cuda core while 1 9800gt 112 cuda core so 112+112=224
your current power supply is perfect for single gtx 460
later you can sli it.

 

[nforce4max]

of course gtx 460 is a regular use for gamming
1 gtx 460 is better than x2 9800gt becuase gtx460 have 336 cuda core while 1 9800gt 112 cuda core so 112+112=224
your current power supply is perfect for single gtx 460
later you can sli it.

Fermi shader is not equal or greater when compared to older architecture. With Fermi Nvidia sacrificed single precession 32bit floating point performance for 64bit double precession for a limited range of applications. A typical gtx 460 averages around one Tflop while a typical 9800gt is just half that. In sli there are losses in overall performance so 100% scaling is not seen. A ref clocked gtx 460 is only slightly faster than a ref clocked gtx 280 and it only has 240 shader cores. 20% is what you will see at stock clocks but once you overclock that will improve.

Cards that I got but not a full list.

Two 7900gtx duo
7950gx2
8800gt
8800gtx
Two 9800gt
9800gtx+
gtx 280
gtx 460

So yes I am a collector and a gamer so I know how these cards actually tend to perform even at the worst of times.