Here's some Honda letters that do make sense; R, VF, VFR, CBR and CB1100R. Although it doesn't apply to the SOHC universe, I always assumed that R designated race-type. VF bikes stood for V-patterned Four cyclinder motors, whether a VF750C (a la 'Custom'), VF500F (same concept as the '79-'83 CB-F bikes?) or VF1000R (race-type). VFR was the logical progression when all VF bikes evolved to race-type. CBR and CB1100R are self explanatory, given the CB moniker.
Just to mention, I have no clue what GSX may stand for, but I beat Suzuki intended it to go fast when they specified it as GSX-R.
And having personally owned a CM400T for 8 years, I can tell you it must stand for City Motherf!ck!ngpileofslowcr@p.