Well, I finished installing the shock and have been riding around on it a couple of weeks now.
The height at the rear has raised 20mm (unladen).
The new shock has allowed me to set the laden sag to a reasonable level of 31mm compared to the 60mm with the stock shock with preload fully cranked up. I could reduce the laden sag even more with the new shock, but I think 31mm is supposed to be about right.
I've got the compression and rebound damping at their middle settings.
Anyway, it seems to be a significant improvement over the original, I haven't had any spine-compressing jolts when going over bumps and haven't scraped the exhaust or centrestand in corners which happened all too easily with the stock shock.
I tried the Z750S fork springs briefly, but I think they are in fact too stiff. The stock ones aren't way too bad, at least they don't bottom out with the preload correctly set.
I'm not a racer and don't know how to fine tune suspension. That's something I've still got to learn. But it's good enough for me as it is :)
Here's a few pics of the shock installation.
http://s38.photobucket.com/albums/e118/edorp/bandit%20shock/Oh yeah, I also discovered the tool kit under the pillion seat. It was a surprise, I didn't know b4's came with one. Looks like it's never been opened.
On another note, I took the bandit to a trackday last weekend and managed to low side, I guess due to trying to lean the bike over further mid corner to tighten my line and the new, commuting rear tyre disagreed with me. The bike is pretty much ok, the brake lever broke, but I had a spare. The front indicator stalks broke and the right handlebar bent (the turn was left hand and the bike flipped onto its right side when it met the dirt). It's got a few new scratches on the crankcase and tank, but overall I think it did pretty well! I was able to change the brake lever, tape up the lights (and my riding gear) and keep on riding. I just have to find a new set of handlebars now when I've got the time.
Next trackday I think I'll try and get leathers rather than cordura riding gear and stickier tyres rather than commuting ones... ;) But that's going to have to wait till I've finished uni at the end of the year.