Will my PSU support high end cards

Yes you will need to upgrade your PSU. If you look at some of the graphics card in that series you find that the min i found is about 500W so you might need to get a PSU of 600W maybe more depending on how much money your willing to spend and if you want to crossfire them
 
No way you can get the 7970. Even the 7870 would be pushing it. I use a 750W for my 7970 (Dont need it but have never had power problems when under full load). You should probably go with a 600W to be sure.
 




Yes he can. I have a 7970 and I have a Kill-A-Watt meter to measure the wattage the power supply is pulling from the wall. On full load of both CPU and GPU, I use only 350W. 350/450 is 78% load on the power supply, in the safe limit and at the most efficient point.

I would not trade a gold 450W power supply for a 600W bronze.
 


Seriously? If it works for you then I guess it should be fine for him. I think that having the extra power is good for OC and full load but if it works for you then I guess. 80+ should help.