The R-Hop should be the most consistent way of doing things because there's no structural weak point like you have with traditional nubs. Maybe their handwork isn't so good, or maybe it's just that the barrel isn't all that decent. I'd say 6.08 is probably wide bore, and anything below 6.04 is tight bore. Stock barrels usually come somewhere in-between.
Accuracy-wise the only things that should have an affect are the hop and barrel. Unless you're getting fluctuating FPS from somewhere like a bad seal (though I'm assuming you've checked this). As RR01 has said, maybe an R-Hop patch isn't the best approach given the slightly novel A&K SVD hop, though I would say that one could effectively have a fixed hop by just replacing the R-Hop and sanding as normal until the required amount of material is sticking into the barrel when the hop is effectively off (relying on the old bucking to apply uniform pressure). Again, this means effectively a fixed hop, but if you're not switching ammo weights then this may be the way forward.
First though, make sure the FPS isn't all over the shop (honestly with a sniper rifle you want to be +/-5 or less shot-to-shot) then check your own patch to see it's not been unduly worn or poorly fitted and then get that new barrel. If you don't want to R-Hop it (though it is easy to redo if you use RTV) then obviously go the classic route, but I've still not seen anything out-perform the R-Hop patch yet. Flat hops come close, but they still don't have quite as much surface area as a patch.