Pedal Suggestions/Help/questions

[IrrelevantD]

I'm going to be building up a Crockett over the weekend for general use. Mostly gravel/trails/chasing my kids around the park stuff, but I'm planning on spending some time on the road getting to the gravel and trails. I'm not going to rule out the possibility of a race here or there, but that's not the primary goal.

I have an old pair of Shimano PD-M515s, which work fine, but my complaint with 2-bolt SPD has always been that they don't feel as stable side to side as road pedals. On road I've been a big fan of wide platforms (SPD-SL and speedplay) with stiff carbon soles. My previous experiences with SPD has generally been with more flexible nylon/plastic soles, so I have a pair of Empires on order in hopes that they will be as stiff as the Factor Techlace I'm using on the road (both are EC90 soles).

My question is this... Given a good stiff shoe, which I'm assuming the Empire is, how much of a difference will I notice between my old M515s and say a M8000, and would I see any additional benefit going to something with a larger for/aft platform such as an M530 or M8020?