I have no comparison for the pivot, since I don't think I've ever even touched one, let alone ridden one, but I definitely have some time on the blt2 my roommate owns. He has a moderate AM build with 2.35 tires, rp23, a vanilla rlc 140mm 15mm QR axle, DH bars, etc, that hits around 31lbs (maybe 30.8 or something).
I've had a pretty significant amount of ride time on that, I've only demoed a roscoe once. First off, I should say that while I think the dual chamber setup on the shock the roscoe has shows alot of potential, it didn't really wow me in any way, I'd much rather have the linkage setup correctly around a progressive shock (like the BLT2) has, at the moment anyway.
I'm a really big fan of ABP I suppose, I like the low single pivot with a floater setup, but I feel like the roscoe could have stood to be a little more plush and higher in the front end. It felt to me like long travel XC bike, where the BLT2 has proper geometry for cleaning gnarlier lines that you want to do in a 140mm bike that you would normally steer clear of on a light weight 100 or 80mm bike.
The roscoe definitely mantained traction in braking a little better then my roommates blt2, but depending on where you stand, brake squat can be a good thing or a bad thing. I'm actually a big fan of a little bit of it, because it keeps the geometry more stable and I don't like the feeling of getting pitched forward, or having the back end lift up and the front sink down. Of the two bikes, I feel like the BLT2 maintains its stability a little better under braking, without getting excessively harsh. I feel like the ABP makes you feel less of the trail while you're braking the the BLT2 does, but at the cost of getting pitched forward a lot more. I give the edge to the BLT2, because it really doesn't get harsh like many single pivots, and I like that the geometry stays more stable, but you'll have to ride both and decide for yourself.
The BLT2 pedals better in every ring, hands down. I can run more sag with the BLT2 and have it still pedal better. The Roscoe I played with I tried running everything from 10-30% sag, and it felt best around 22%, but even then it never pedaled as well as the BLT2 (in any ring, including the granny ring, which VPP traditionally does not pedal well in)
I should explain that I feel like there are two types of bikes that both "pedal well" but do so in very different ways. Some bikes kind of "lock up" and pedal like a hardtail. You never feel the shock moving if you're pedaling. This isn't really my thing, but it works for some people. Old style VPP, and low/mid single pivots tend to do a similar thing (when you're in the right gears anyway). Then there is the type of setup that doesn't seem to move when you pedal, and stays stable, but the shock seems free to move up and down all the same. When you pedal up/over rocks, the wheel goes up and down and tracks over them, rather then making the bike go up and down like a hardtail.
The VPP2 the BLT2 uses seems to be somewhere in between. Its definitely not as plush and free to move while maintaining good pedaling as something using dw link or meastro, but its much more free to move then the older VPP bikes I've ridden. Its a pretty good mix of both.
I'm very impressed with how stiff the BLT2 is. The Roscoe was reasonably stiff, and I don't think it would ever bother me, but I definitely notice the BLT2 is stiffer. I felt like the roscoe twisted a little more where the BLT2 will just deflect and slip, but overall I like that more because thats the tires, not the bike, and you can hold a much more predictable line with the stiffer bike. Both are reasonably stiff for a 140mm bike.
Descending goes to the BLT2 hands down. Maybe because I've had more time on it, but I don't think I've ever shied away from a line I normally do on my DH bike with the BLT2, where I frequently would shy away from really attacking some corners and jumping with the roscoe. I feel like the steeper HA coupled with the the getting pitched over bars when braking, made a huge difference, and the bike just never felt like it tracked as well as the BLT2.
The one place I give the advantage to the roscoe is the HT/fork, that tapered setup it has is quite noticeable.
Overall I like the BLT2 alot more. It does what I want a trail bike to (be efficient, make it up the hills easily, but still be a treat to ride down or hit up the fun features you see along the way), where the roscoe just feels like an inefficient XC bike.