Yeah I got some Shimano MT42s on the weekend, with the 51 SPD cleats, and jumped straight into riding my wife's M324 equipped bike on the Monday.
Clipstack on Friday... ironically, the first time my wife rode home with me after work 6 months ago as I pulled up she unclipped but I coasted towards her and pushed her to the clipped side, nearly causing her to clipstack. I stacked in the exact same place, within 3 metres of that. I tightened up the clips that morning, REALLY bad idea, because I'm unsure the hex screws are tight enough in my shoes to allow them to break in a hurry. Anyway, I lay on the ground and gave myself a clap, honestly what else can you do? Bummed that I raised the seatpost earlier in the week, so it was a long way down at 6'1" tall.
My report on the improvements - I have a pattern of spinning at 100+rpm seems to have zero lactic acid buildup so it makes for a repeatable ride through the week. I adjust the gears to maintain that pace. I've noticed that I have been going on the flats with zero improvement, slightly more comfort but my old shoes were utterly hammered so that's not hard, but the CLIMBS...
Every single significant climb where I had to drop gears (I'm normally on the big ring, about halfway on the cassette, hills means middle ring for me) I am pedalling 2 gears higher than I normally do. Hell, I climbed hills out of the saddle yesterday in the big ring and 7th gear, that's like downhills normally LOL
Go clipless. You'd be insane not to if you do anything beyond a quick poke to the shops. It's just so nice to not fight against the hills anymore!