A stock GTX 480 draws 250W at max according to the Nvidia website:

http://www.nvidia.com/object/product_geforce_gtx_480_us.html

Then there's the CPU,which is 130W at stock, so there's 1130W not counting overclocks and other hardware.

To be honest, I'm uncertain if even 1500W would be safe for that kind of hardware unless it was a really, really good 1500W power supply. I would say otherwise if it weren't for such a high overclock on your CPU and four overclocked, power-hungry GPUs. Of course, this is from someone who has never overclocked anything before. I'm just going by manufacturer information.

i think the 480 take more than 250 w

"Is the Silver Stone Strider 1500W enough to run"
You kidding me? Almost enough to run a refrigerator, lol

I have to agree with cvasquez, it's enough to run two refrigerators! :)

My specs:
http://www.youtube.com/watch?v=NXAVnxVnd98