Nothing is ever true with this kind of debate. All lurchers are slightly different, even the best coursing machines.
Same with every hare run and again with every field trodden in. Even when everything looks the same, it really is not. Just far too many variables in every run.
On real soft ground (slop as you lot are calling it) from what i've seen, i've always prefered a bigger, more powerful dog. They seem to drive through and still kick in the gears. Not that i ain't seen smaller, lighter dogs kill hares on sodden ground, i have, many times but i like a more robust mutt for that j