Well, it's late, I'm tired and I think I must have listened to most of the clips on this website but it has been a very illuminating experience. Of the three options I had it down to, the Rebel Yell was just too modern and aggressive. In its own right it's a great pickup but it's not for what I want in this guitar. If I was looking for a Rock/Metal pickup in a mahogany guitar I'd maybe choose it over the Nailbomb because it's not as hairy but like Phil, it's just not my thing.
The clips for both the VHII and Emerald were fantastic and in many ways it's a very hard choice as they're both so good. My choice is down to nothing other than my gut. Both were great but only the Emerald had that 'WOW!' factor when I listened to virtually every clip. Will it be too bright in a PRS? I certainly hope not. Unfortunately, all of the clips that specified the guitar used involved some sort of Les Paul so perhaps I'll be pioneering new ground by putting one into a PRS but it sounds so good that I think I need to at least give it a try. What really tipped me over the edge was the clips I put a link to and the one Phil posted a link for. Between those clips the Emerald seemed to cover Slash, Gary Moore and Santana and that's three of my favourite tones. I think I have the money saved for them now but I may need to wait until I'm paid. I'll check in the morning and order them asap.
Many thanks to everyone who has helped in this difficult choice. It is very much appreciated I assure you. Now let's see if I can get mine installed before Phil does his :D