power consumption proportional to workload?

Is power consumed by video cards roughly proportional to workload?

I'm about to build a new PC. I'm not a gamer, but would on rare occasion run Flight Simulator X (FSX) and would want it to run well. I'm considering a GeForce 8600gt or 8800gt. The 8600gt is said to consume 43 watts, whereas the 8800gt is quoted at 138 watts -- a huge difference. ( http://en.wikipedia.org/wiki/GeForce_8_Series )

I'd be willing to pay for the 8800gt for a good experience with FSX, but am not willing to pay for, or withstand the heat of, 138 watts if it consumes that even for browsing and office applications. So:

1. Does the power consumed reduce considerably for office-apps type of workload?

2. Would the power of the 8600gt and 8800gt be comparable when used for office apps?

3. If so, are there any figures for the 'baseline' minimum power consumption for both of those types of card?

4. Finally, a somewhat different question: Would the 8600gt provide a sufficient experience with FSX set to high, but perhaps not maximum, settings? (Assume an e8400 CPU.)

Thank you to anyone who can help.

wow ^ ^ about the best and most thorough answer i've ever seen.

JaguarSKX,
Your answer is a GREAT help; MANY thanks. I google'd and google'd and never found anything close to the idle power consumption chart you supplied.
[FYI, I'm cost-sensitive. The 8800gt is now down to about $140. That's still a big gulp over the $60 for an 8600gt, but I'm not sure I can stretch much further, but I'll look at the other possibilities you mention.]