I use both. The SL+ is much thicker sounding to me and I use it for my solos. I use the 1086 for rhythm, it seems thinner but has more of a heavy modern sound to it. Gain wise I think they are about the same, the SL+ has much more gain than I thought it would, and the 1086 has less than I thought it would. The SL+ is more mid sounding, at least "good" mids anyways. If I turn up the mids too much on the 1086 it sounds crappy. If you're looking for a more classic, thick, mid to high gain I'd say go for the SL+. For more modern sounds, go for the 1086...but I'll add that I think the Lynch Grail has a better tone for modern metal...and a modded 1086 is said to be about as good as it gets for monsterous gain and tone.
Greg