Power consumption: Radeon HD 4870 x 4670

I'm assembling a new PC:

- Mainboard Asus P6T
- CPU Intel Core I7 920
- Memory - total 6 GB, kit of 3 X 2GB, DDR3, OCZ (P/N: OCZ3G1600LV6GK)
- Power supply Seventeam ST-750 Z-AF, 750 watts
- Graphics card Xfx, model HD-487A-ZWFC, 1 GB DDR3, based on ATI Radeon HD 4870
- HDDs - two Seagate ST31500341AS (1.5TB, Barracuda 7200.11 SATA II, cache 32MB)

I don't play games. Never. But occasionally (say, once a month) I edit HD 1080i video files from my camcorder (Canon HF-11, AVCHD) using Studio 14 and Adobe Premiere CS4. And of course I like to watch the rendered files (all HD, 1080i) afterwards.

So, most of the time, this PC will be used as a general purpose machine, but from time to time, it will be called to provide high performance.

At first, I thought that the above mentioned graphics card would be adequate to the rest of the system. BUT, when I read about its IDLE power consumption (55 watts !!) I became very disapointed.

Of course, nobody likes to continuously waste 55 watts (minimum) with the video card alone! (the maximum, worst case consumption is around 187 watts, but what matters in my case is Idle consumption, of course).

So I chose another one:
- Xfx, model HD-467X-ZDF2, 1GB DDR2, ATI Radeon HD 4670

This one spends 8 watts idle and 64 watts at maximum. A big difference.

My question is: if I choose the HD 4670 in order to have a smarter power solution, will I still be able to easily edit my personal movies? Or will I really need the power-hungry Radeon HD 4870?

Thanks for any help and please forgive my poor English   .