Hey Garfield. They basically ride almost identically
The R5 is actually a teeny bit harsher. The only reason I have two so similar bikes has to do with a repair to the R3SL frame I needed to make last summer. While I was waiting I bought the stupid expensive R5. Now the only real difference between them is I use a standard crank on the R3SL and a compact crank on the R5.
It's always nice to have a backup bike, but it's also nice to have a little variety. Oh well.