I have the normal for 4x5 two 15 cm rails on a 30 cm bench. Since adding an 8x10 back, I have an extension rail to the mix probably about 20cm, but it's at home and I'm not. Both standards fit nicely on the 15 cm rail, and that's a great way to carry the thing around. Given that, I think your 'asymetric' idea would work well.

Like others here, I'm using this camera screwed directly onto my tripod with no head. I find it a bit inconvenient because the tripod is an old bogen with a geared column and the rail does not line up nicely with the legs and the column doesn't rotate. It makes for a good sturdy platform, but not really possible to aim the camera very far from level. I might get one of those 'leveling heads' one of these days. I think *for me* it might make good sense.