The SLI is a noticeable upgrade over the X1900XTX. It really depends on how much the 2X 8800GTS costs. If it's anything more than $250, you might as well get a HD4870 or a GTX280 (then you don't need to even change your motherboard).
For free, I would take them although I probably would not upgrade to an nVidia based Mb to SLI them.
A single GTS 640 will outperform your XTX and should be a decent free upgrade.
A quick look at Tom's new GPU charts (just when you think they couldn't get any worse ) shows SLIed 8800GTS 320 (there are no comparisons on SLIed 640's but they perform similarly) mostly falling between a 4850 and 4870 when the game scaled. When the game did not scale, it would fall behind the performance of a 4850.
For the cost of your upgrade, motherboard, RAM? (bye CL 2.5 I am assuming you are running PC3200 or similar?) and probably a new PSU, you might as well get a better performing 4870. If nothing else, I would upgrade to a P45 or X38/48 Intel based platform and run a single GTS 640 until you can afford another GPU upgrade. At a moderate resolution (1680x1050 and below) a single GTS 640 still has plenty of power and should provide a more than adequate gaming experience, IMO.
You should try the single 8800GTS and see how you like it. It should be a decent upgrade from your current card. You could sell the other and keep your money in your pocket for an overall upgrade unless what you typed below in parenthesis is your hardware:
I am changing my system and have offered my son (bios2) for free! the following spec components:-
Asus Cross-hair board
2x XFX 8800GTS (640mb) SLI Cards
3.25Gb corsair xm dominator pc2 6400 DDR2 Ram
AMD 6000+ 64 x2 dual core 3.01ghz CPU
My sons existing MB = XFX 670i ultra
2gb TwinX XMS2 PC2 6400
Quadcore intel Q6600 G0 CPU
Radeon X1900XTX 512MB
What he wants to know is given his CPU is faster than my old AMD is it worth swapping his old components for mine?
Am I being stupid or does he not need to change his MB? Its a 670i board, surely that means SLI is no problem?
@ bios2, I'd take both the 8800's and some of the RAM to make 4Gb. Overclock the q6600 to say 3.2Ghz and that'd be a pretty nice gaming system. The 8800's can also be overclocked should you need a touch more performance. (can you tell i like overclocking?).
I think there must be a typo there.
Guessing you probably ment 650i Ultra which does not support SLI.
If I had to chose between those two systems (and could not overclock I assume) I would go with the AMD SLI system.
For gaming, the AMD X2 6000+ is staring to get old but it still has nearly the same amount of power as a stock Q6600 in lightly threaded apps. In this situation, the more powerful GPU setup will net higher performance than a single GPU and a more powerful CPU.
If the typo goes the other way and you have a 680i based Mb, rip the two 8800GTS 640's out of the AMD platform and pair them with the Q6600.
Now here is a question I (Dad) would appreciate an answer on. I have been building Pc's for many a year and have always gone OTT (That's over the top for my American friends) with the components I use for my own needs (My lads now build their own Pc's for gaming and so I will be able to kick them off my machine at long last)
I do not play games and use my Pc for playing music, films, video editing internet etc. I have spent a mint over the past 10 years on a home cinema system that would blow away your local showcase but that's another story.
So now that my new build has no requirement to be the dogs thingies when it comes to playing games perhaps you could comment on the proposed items:-
CPU Intel 2 Quad Core Q9550 2.83ghz 12 Mb cache (hope this doesnt scream like my old Amd 6000+ Watching Dvd films was a pain)
Nvidia Geforce GTX 260 PCI-E - (216 Cores) This appears to be a new top end card without the heat, noise and power consumption compared to the ATI/AMD boards or indeed the GTX 280
Asus Xonar Hdav 1.3 \ Deluxe True HDMI Soundcard (When will graphics cards be able to stream uncompressed 7.1 via HDMI? )
New Blueray Dvd player - any recommendations?
My old Pioneer Dvd recorder
My old twin Western digital 160 gig hard drives WD1600YS Cav re. Sata 300. 16MB Cache. 8.9ms. running on a RAID set up.
Nebula digital Tv card. so I require a std PCI slot
Can you suggest a quality MB and Ram to suit the above components? given Home cinema is my hobby
As I hear Ati's AVIVO is actually better (and free) compared to Nvidia's Purevideo, so I'd check out Ati cards instead. If you're concerned about Ati cards temperature, then you must remember that they are being built on the newer A12 silicon that is designed to sustain those temperatures, but you can always get a non-reference cooler model (Sapphire, ASUS, HIS, and Powercolor come to mind) that can get those temps really low (that's what I did with my HD 4850.)
I'd go with the Q9550, but get an aftermarket cooler (Xigmatek HDT 1283 with Noctua or Scythe S-Flex fans come to mind) with a silent fan, that way you won't run into any noise issues while playing your favorite movies.
One more thing I'd like to suggest you is that since you are a video enthusiast and I'm sure you want to see full HD videos, those take a lot of space. Given the fact that you are already planning a RAID array, I'd suggest two Western Digital 640GB drives to provide you with all the storage you'll need.
If you do decide to get an Ati card, then I'd suggest a nice P45 motherboard or maybe even an X38 board (X48 isn't worth the money, since it has almost the same capabilities as X38s, but with a $150 premium on them). And 4GB of DDR2 1066 ram.
Links to products I mentioned:
Western Digital Caviar SE16 WD6400AAKS 640GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM