So how does their sizing run?

looking at the Impact 2 lows. Normally a size 8, but recently bought some running shoes in a 7.5 which i think are a better fit.

Do 5-10s run big/small or pretty accurate?

They pretty much match my other trainers. I ordered a pair of impacts and a pair of freeriders off CRC, the impacts felt quite tall/thick, which seemed odd given the current trend for skinny pedals, so I sent them back and kept the freeriders.

I wouldn’t go too tight with bike shoes as your feet swell as they warm up.

That’s the first time I’ve heard of someone going down a size in running shoes.

My 5-10’s are bang on with my regular trainers.