In reply to gavjwp:
If you have older Friends, the size 4 sits somewhere between the current Friend 3 and 4. I have a full rack of Camalots and carry my single-axle Friend 4 on occasion as a size '3.5'.
Your 3 main options for the size I think you are looking for are now:
DMM Dragon 6, Wild Country Friend 4, Black Diamond Camalot 4
Wild Country brought their size numbers in line with BD when they moved to double-axle units that are basically clones of Camalots.
The Black Diamond Camalot 4 (same size as Dragon 6) has a couple of advantages over others in my opinion:
Thumb loop - pretty necessary on big cams for me (DMM Dragon does not have, WC does)
Non-extendable sling - extendable slings do my head in (both WC and DMM have them)
Retaining clips - BD is the only unit with them, as far as I know. Neat little invention which holds the lobes retracted until you deploy the cam. This cuts down the size of the unit on your harness
Reslinging - BD resling at cost of postage for EU customers currently, DMM currently offer a good reslinging service, WC eventually succumbed to mounting pressure to announce this service but it is not something they currently offer (and considering they are being selective about what they resling and have not released any more information on when, where or how their operation will be running since it was announced about a year ago, I wouldn't hold my breath).
Post edited at 11:41