Buffering Micro-SD data for power saving useful?
There are 4 numbers you need:

A. Power when writing. Assumed 200 mA.

B. Power when not in sleep mode, but not writing.

C. Power when in sleep mode. Assumed 300 uA.

D. Time to perform a write

Power = Voltage * (A*D + (5 ms-D) * B + 995 mS * C).

If D ~ 5 ms; A is dominant.