I am at a point where I was wondering if it is time to upgrade. For the most part I have a decent system evga x58 motherboard 6 gig ddr3 ram core i7 920 1k watt power supply was just thinking would I be fine to update the card and use my 280 for physx or go sli 280s? Tried to do some searching no real comparisons. Play all types of games and am always ready for the latest greatest game. COD WOW are a couple type of games I am into (well used to be).
If you want the best performance for the money, a pair of HD6850's or HD6950's (depending on your price range) offers the best value. Currently nVidia's cards are too expensive compared to the performance that two lower Radeon cards offer, and the fact that your Mobo is x58 is great.
I would be very careful what gtx 560 ti that is bought, if it does not have the mid plate or any meaningful cooling for the power vrm and vram it is not worth it. The 6950 on the other hand are usually come with a mid plate if you buy a reference model which do have the dual bios which are great for the flash if one ever wants to go down that road but not the default choice for owners of this card. The 6950 in the traditional two way crossfire with one or two monitors offer more than enough power even for the most demanding games except for those that have physx enabled.
Reference yes to either option but be very careful what you settle with and not all are created equal. If no power vrm cooling and little or no vram cooling it will not last as long as you may like.