The Acerbis tank arrived today. Here's my comparison:
5 lb 6oz with petcock and mounting hardware
NOTE: when you factor in the .3 gallons of unusable fuel that the Clarke tank carries, the effective statistics become:
See-thru so you can tell how much gas you have
Cheaper of the two tanks
One petcock - you have to stop and lean the bike over to use the right side gas.
Wide - probably would be uncomfortable for a standing rider with knee braces.
Kit does not include a petcock
A fair amount of grinding had to be done to fit the stock petcock
The tank rubs on the decomp cable
Carries 2lb 1oz of unusable fuel (below petcock, seen below)
It should be noted that some people have run a tube into the low point of the Clarke tank and used a fuel pump to extract all the fuel.
6lb 14oz with petcocks and mounting hardware
Easier to remove/reinstall (better fit)
Two petcocks - no leaning the bike over to access your reserve supply
Narrower for a more comfortable fit
Only comes in solid white - you can't see how much fuel you have left
Two petcocks - more things to break
My kit did not include a "Y" fitting to connect the two petcocks, but apparently this is normally included.
More expensive of the two tanks