jwscud,
sometime ago while balancing fuel I accidentally turned off both fuel pumps from one tank prior to opening the fuel crossfeed valve. This was at 41k. I realized immediately and opened the x feed valve while staring at the engine parameters for the longest 2 seconds of my life it took the crossfeed to open completely. The left engine did not show the slightest sign thrust deterioration. The suction feed is quite reliable.
And again, if you lose both your AC sources at the same time, either someone is trying a new electronic weapon nearby or you are a very unlucky fellow. IŽd go for the 2nd.