What other mods has the engine had, and is it a 350 or a 400? From my experience with Yoshi ST-1 Cams, which are a very similar mild cam to Web's Street Cam and the Megacycle 131-00, just changing the cam doesn't make much difference at all on an otherwise stock 400.
Alternatively, if you do have some engine mods, you may be better off considering a less mild cam- something like Joy Cams' Yoshi St-2 or Isle of Man grinds, to get the most out of your engine overall.
You'd probably be very well off posting this question to the yahoo group,
http://autos.groups.yahoo.com/group/cb400f/ , as the cam options have been covered on there before & one guy, Jeff Chenevert, researched it very thoroughly a few years ago.
