Yeah I would agree.
The more powerful the components, the bigger the PSU would have to be.
I've got a Quad Core and a 500GB HDD, and with a GTX 260 and I've got a 750Watt PSU. If I was to upgrade to a GTX 295. I'd need a 700+ Watt. You get what I'm saying?
The more you go up, the more power you'd need.
If you post the specs your looking at, I'm sure someone here would kindly help.
Also, a 700Watt is ampful enough for what ever you plan to do I say!