I'm sure it had nothing to do with the flash, just thought I'd be as descriptive about the events in case it helps somewhere along the lines.

I'm actually quite stunned the battery lasted so well, it was still showing as full (ok its only got 4(?) blocks) after a good 8 hours use, 6 of which were spent with the tar operation going. Something clearly wasn't right as it should't last that long.

Whilst I admit the high speed mmc kernel makes a difference, the issue I had today with slow copying must have been hardware related. Perhaps the new card (Datawrite 120x High Speed RSMMC) wasn't happy, I'll run some checks on it later. Perhaps I should have found some MMC Mobile instead (no idea of the difference tbh).