I'm not so sure I'd go for the bronze ones, true, they might add to frame stiffness, but I'm thinking a lot of vibration will be transmitted through the frame to the rider, some time in the past a PO put red nolethane engine mount rubbers through mine and being some what harder (with the fingernail test) than the original rubbers mine also has vibration going through the pegs seat and bars that my old one never had. and till proven other wise I'm blaming the harder mounts.
In fact I've contemplated discarding them and going OEM spec.
So, Coops keep us updated where who and how much.