Forgot to say the cab runs on 8ohms if that narrows it down?!
the cab is whatever the speakers are (combined with the stock wiring), so i don't think it really affects things. Assuming it's the usual series/parallel combo that most 4x12s seem to use, you can pretty much use anything.
that being said...
is the cab any good? It's definitely one of laney's cheaper cabs- is it even ply? if it's not ply i'd just sell it and buy another cab. If it is, it might be worth upgrading the speakers, but four decent speakers are likely to cost you the guts of £300, which is not far off what decent 4x12s with decent speakers cost. Granted if you buy your own speakers you have more choice (as most cabs with decent speakers have v30s), but yeah.
for what you're playing i'd maybe try greenbacks with g12h30s. v30s sound pretty modern to me (though some of those combos which have been mentioned are very nice too, and do tone them down somewhat/a lot). the g12t75 is very nice combined with them, too, but again is a bit more on the modern side of things. Not metalcore modern, but certainly 80s thrash/hair metal type of modern.
EDIT: i've been on a bit of a speaker binge recently, lol. If you're in no rush, I was thinking of ordering another couple of speakers tonight, so you can wait to hear what i think of them. Or else just search in places like tgp and harmony central to see what people think.
if you want to keep the cost down, the eminence gb128 is meant to be pretty nice, but i haven't tried it yet (it's one of the ones i was going to pick up), and is supposedly pretty greenbacky.