Possibly SLI'ing Two GTX 560 Ti's - Help!

[Awesomedude2142]

My PC:

[B]CPU[/B]: Intel Core i7-950 (Overclocked) @ 3.8ghz
[B]GPU[/B]: GTX 560 Ti (PNY)
[B]RAM[/B]: 6GB DDR3 @ 1600mhz
[B]MoBo[/B]: GIGABYTE X58A-UD3R
[B]Case[/B]: NZXT Phantom
H50 Water Cooling

Hey, so im thinking about SLI'ing two GTX 560 Ti's, because(basically just for a few years future proof) :

[B]Cost[/B]: Both 560's will cost 520$ total (including the 560 i already have), when the 580 is around 540$.
[B]Performance[/B]: The 560 preforms around 25-30% lower than the 580. So, if i SLI the 560, ill get better performance for slightly less. (Now, a friend told me this, but he's even better with computers than i am: That with SLI, you can except about a 70%-100% performance increase. If thats true, then ill get atleast 40% better performance than the 580, and the SLI 560's may be up to par with NVidia's next GPU. Not sure though)

Basically, if i do, it will cost less and preform better than the 580 and may be equal to the next GPU NVidia comes out with. Only thing im worried about is that in 2 years, NVidia will come out with the GTX 600 or something, but even then, i probably wont have enough money to get that (would obviously cost over 500$) unless i get a job (i just turned 15 on June 30th)

I have the [B]700W[/B] Corsair PSU, of which im only using about 500W max. So, add 135 to it, and still under 700, so power is good. Heat is fine, GPU is around 35*C idle, about 45*C gaming (Gonna get another 200m fan for the side of my case if i do get another 560). Yes, my MoBo does support Dual and Triple SLI (i could have 3 SLI'd 560's if i wanted to! lol)

If you need any more information just ask.
Thanks

[Reapaninja]

if you don't need the power right now, don't bother
prices will only drop