Wow for me the SL+ didn't come close to the gain I got with my 1086, interesting. I really dig the 1086, it just has alot of versatility with what you can do with it compared to the other modules - but it is a newer rock tone definitely - some like that and some don't, just depends on your cup of tea.
I just purchased a Modern through Steve here on the forums and got to play one of these a few months ago and really dug the tone from it. It doesn't really sound like any amp out there I can put my finger on, but it is unique in its own right and I guess that is why I liked it and bought one finally.
The SL+ is nice and so is the XTC in my opinion, but the SL+ is gainier compared to the XTC, where as the XTC has a smoother tone articulation wise not as harsh.
I agree with another post on the Ultra series, they do seem compressed quite a bit - but are great for those Dimebag type tones if you dig that (like me). The XL seems to have a bit more gain and a tighter sound overall compared to the original Ultra, but are both very close in sound.
I am waiting on my Grail, which should be here this week - and from what I've heard it is supposed to be a "better" rectifier tone than the Recto and Rectified modules - but once again that is just what I've heard from some people. I own a Dual Rec so I will do a side by side comparison when it comes in and post my results then.
Hope some of that rambling helped lol.