I mostly am a SETI guy.
On a fast machine with lots of ram, that is all I run, all the time.
SETI is too much of a pig on my slower machine, so when I'm on it, I run RC5.
SETI only runs in the "screensaver set to blank mode" on this one. When SETI runs RC5 gets no resources.
If SETI does not get a work unit for any reason, RC5 will run.