Yes, with softth I got some noticeable (but bearable at least for me) tearing in left&right monitors but central monitor is fine. If becomes unconfortable, I would switch to th2go + 2x19" (I have got already from my previous rig) + 1touchscreen.
A bigger problem is a bit of unstability with SoftTh-BS, especially agravated with some options of softth (multihead and using different resolution for left&right mons increases chances of not running at all, but when works, it does all the time till I quit the sim).
Later, first I have to install Win7, overclock as far as I can, configuration of hotas, fourth monitor (7" touchscreen) with touchbuddy and test a couple more things.
It´s all about cpu and pcie bus, and BS is not particulary good looking and demanding sim (in graphics). SofTh penalizes heavily cpu, and BS is a very cpu hungry animal. Because of that, I upgraded first (before gpu) cpu&mb (i7 and a 2x16xPCIE).
Anyway, I tested a quick overclock (one easy option in MB) to 2.92GHz just to get a look, with no fps gains at all . It was a little dissapointment, but I still have left the real OC (I expect minimum of 3.8GHz).
I think maybe 295gtx is lowering your frames (or not, particulary if you play with high AA), because SLI taxes cpu heavily, and we know how important is cpu for BS. Try to deactivate SLI, to see if there is any change on performance. After my tests, I cannot be more sure there is a giant cpu bottleneck in BS.
I´m about getting a 285gtx, the most powerfull monogpu. If my fps don´t get higher in BS, at least it will do in some games I like. Also I get more vram room (a)
Latest versions of SoftTh (1.09) works with IL-2 (directx mode). Also, there is a FOV changer for it, so use3renders option is not a must now and makes it compatible with HDR mods (with use3renders, hdr is only applied to central viewport-monitor, with left&right mons untouched).
I also have th2go and I´d said that if you want resolutions of 3x1680x1050 or less, th2go is waaaay better in general (but softth is more flexible) than softth and I think it worths the money. In this sim, I estimate (after some more testing with th2go) th2go has 30-80% more fps than SoftTh, and configuration and compatibility is very far away.
I like softth for BS because you can see shkval and abris with a very good res in central monitor at 2560x1600, and have the option to lower left&right mons to 1280x800 (for ex), which anyway is just like 2x2 SSAA (the best kind of antialising), regaining some fps, for peripheral vision.
Note: it´s curious that performance of BS in 7680x1600 is a lot better than IL-2s. I remember about 10-12fps max-min detail in IL2 with the same resolution. Maybe because It´s not a native directx game and works with a opengl wrapper.
One more image: loading screen