I never detected a 75W surge but that doesn't mean it can never happen.   I think the "it pulls 75W" nonsense comes from the fact that the spec allows UP TO 75W. Some cards might pull 75W (probably ones which lack supplemental power connectors) but the 5970 doesn't.  The max I got was ~30W and that didn't occur until after mining has started.  I measured it for about a minute or so and it remained in the 27W-30W range.

Actually at startup it only pulled about 12W from the slot.  By the PCIe spec only PCIe 16x devices can pull >25W only once they have been identified (via bus interrogation) as high current device.  No device is allowed to pull >10W until identified.  I guess the card with 12W @ the slot on startup was slightly over spec.