Alright, so i've searched and searched but the only conclusion i come up with is that the RPM is "more darker" and the RBI is "more laid back". What the heck does that mean?! haha. I have a Rickenbacker and a GK2001RB. I'm not 100% sure i'm getting a Sansamp, but like a lot of people in the effect forum now- i like knowing my options So what i've gathered is that the RPM has more control over the mids. The RBI does have Presence, but i hear it's too clanky- I don't want my Rick to sound like a stingray!