My expierience for SS and not FG (Though I did run FG for 1 season and it was not to my liking).... SPD's (and the variants of the SPD cleat made by Ritchey, Welgo,etc) don't have a ton of clamping force. I semi-regularly un-clip from stop-lights when applying full downward and lifting force. Its always my lifting foot that unclips uninentionally, never the downward foot.

Just want to make the distinction, SPD-SL (LOOK style cleats) never happens.

Not sure what kind of forces are invovled in skipping/skidding, but be aware of SPD's limitations.