The 560TI is not the only upgrade coming 'round the bend. We have the 7000 series coming out 'before Christmas' (granted after the delays of the bulldozer release we begin to wonder if they mean this Christmas or next Christmas), and then the nVidia 600 series coming out this winter/spring. After that things may quiet down a little for the summer.
It is times like this that we need to remember that things will always improve, and will always drop in price (except for those damn F4 HDDs I was about to buy before everything went underwater!). Build with the expectation that your computer will be 'outdated' within 6mo. Build with a purpose in mind, so that it will do what you want it to do over the next 3 years. The real questions should be:
1) What am I going to use the hardware for (Now, and in 3-5 years)
2) Will it perform as expected for the things I will use it for
3) Are the things I really need it for out yet?
4) Will the next gen hardware provide a significant (20% or more in my book) increase in performance for a similar price point? (ie, you will not notice 1-5 fps difference in performance from a product refresh, but you will miss 10-20 fps from a new product line)
In regard to the last question, the next gen hardware may be worth waiting for as they are new architectures from both AMD and nVidia, which tend to give a larger performance boost than a simple product line refresh. Plus the new cards from both houses will be less power hungry, which means (generally) more overclock-ability, or less heat/noise in the case.
Granted, to take real advantage of the new cards you will need a new platform with PCIe3, But I am sure the first cards out will not saturate the PCIe2 interface anyways, especially in the mid-range cards you are looking at (the 580 only takes ~60% of the PCIe2 bandwidth, so even with a 25% increase in performance the 680 would only take ~75% of PCIe2 16x, which is fine for a single card config, and in reality the increase will likely be smaller than this). But you can buy a PCIe3 card when it comes out soon, use it in PCIe2 with a minimal performance hit (if any), and then SLI/xFire it later when you can afford a new platform with PCIe3.
All that said; The 560IT and 570 are great cards, and I doubt that you would regret either purchase. I almost bought one myself (the 570 as it has mercury playback engine support) before I decided to wait for IB to come out, later to find that the 600 series would be out by then anyways. But then again, I'm the type of frugal bastard that waits for all the game expansions to come out before starting a game, so I wont be playing the new blockbuster games for about a year anyways, if you want to play the new games when they come out then I suppose my strategy wont work so well
Waiting for something is a good idea. But for now i think you're too close to GTX570. And since you are planning to upgrade the monitor soon then GTX570 is a good option. Also if you want to change it later on... Ebay is always there to sell the GTX570!
GTX 570 is the sweet spot right now and especially in BF3.
the price difference compared to the GTX 580 for just a few frames is not worth it.
yes the GTX 580 rocks and I want one but I will be more than happy with the GTX 570.
and the GTX 570 in SLi is killer..
I say go for the GTX 570 or wait until the GTX 6-series is released and hold on.
I however have the itch to upgrade regardless of what's coming.
I would say upgrade and don't look back. The only thing is GTX 570 Vs 560Ti. Price wise they are 1/3 apart (Europe prices, comparing same manufacturer's pricing). Performance wise extra 20% at best. IMO it's just not worth it. Especially since you will probably want to upgrade Spring 2012 to new architecture. I have GTX 560 Ti from ASUS and I am more than delighted with it. Would not swap it for GTX 570 even if the difference was €50, first because of heat, second because of power consumption.