ok first off, what PUps come with an epi Les Paul Standard? and also, is it worth replacing them with Burstbucker Pro's?
I'm pretty sure they're alnico Vs but don't quote me on that. Also if you like the sound of burstbuckers go try out a gibson LP to keep testing but keep something in mind. Epi standard LPs have ALDER in them as well so it won't sound exactly the same.

P.S. I've heard that the cause of muddy neck pickups on les paul is because burstbuckers are bassy pickups put in a mahogany body causing the muddiness so be wary.