Your best bet will probably just to have a play and find what speed and manual feed rate works for you and your router with with material you are using.
Just make sure you have your slotting cutter on the right way round. It does cut if you have it the otherway round, it will just smoke alot (as I found out the other week

)
I cut the slots in my MDF CP ends the other day using the max speed of my router which is ~20,000RPM and fed it fast enough so that the bit did not burn but not too fast so that it was putting excessive load on the motor.
Needless to say make sure you are wearing the correct PPE.