I put together a gear comparison chart a while ago that might be helpful. It shows speeds in gear, rpm after an upshift, and the rpm when cruising at 70 mph for the Caterham 6-speed, the BGH long 1st gear (E2) and two versions of the BGH Sporting close (E7): one with the shortest 1st and tallest 5th, and the other with tightest 1st and 5th combo. The speed in gear and revs at 70mph data assume a 7500rpm redline and 205/60-13 rear tires.
I ended up keeping my 3.62 LSD diff and going with the BGH long 1st gearbox. My engine (210hp 2.0L Duratec) has such a broad torque curve that the 6-speed was pointless, and although I would prefer the E7 for the tighter gap from 3rd-4th, those ratios are really optimized for a 3.92. No complaints.
http://www.throttle-steer.com/uploads/1/1/0/8/11083275/7645517_orig.jpg
-John