I7 950 strong enough for GTX480 SLI?

You are FINE. The i7 950 is about the 4th fastest desktop processor made. You can always overclock the crap out of it as well. It should do ~4ghz on air pretty easy maybe even 4.5.

Thank you very much for the info.
I never overclocked a CPU myself, so I will search the Internet for a instruction how to do it....thanks again.

The forums here at Tom's have everything you need to overclock. You will as a rule need aftermarket cooling to overclock much and you are crazy not to overclock because doing so will make your i7 950 more powerful than the $1000 Extreme Edition chips but even at stock an i7 950 will not bottleneck SLI GTX480s.
If you will start a new thread listing your exact parts ( motherboard, RAM, power supply ect. ) I am sure someone will get you started.

Check the OC'ng section and you'll find some useful guides
http://www.tomshardware.com/forum/forum-29.html

At stock clocks, it depends on the game. If you overclock it though you won't have to worry about your CPU being the limit for some time