We're at cross purposes here - I'm not trying to make an ultra wide picture by stitching, but simply wanting to dramatically increase the resolution for bigger images, and would just use a normal 135mm 4x5" lens (of the very best quality) that's all.
If I use the Kapture Group I get 4x P45 files stitched together for far greater resolution/ big prints. i.e. about 440Mb in 8bit, 880mb in 16bit.