since you have been all thru the drive train and it is not sorting out, it seems that (with what you changed out) it should be getting worse at higher speeds or that regardless of speed the the sensation should go with the engine rpms. and you are saying its neither.

localized to a speed range and engine speed. interesting.
does it only feel buzzy? handlebars or foot pegs? whole bike. short or long frequency? lopey?

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter