Shwaggy,
I've played around with every effects pedal I own between the line outs on my RT3 & M101 and a keyboard amp. I have used some of those effects including overdrive when recording. I still prefer plain old Hammond growl from a tweeked trim capacitor into a cranked Leslie for the styles I play, mostly blues.
For distortion a Boss OS-2 is flexable, works well and they are cheap, $64.00 from Musicians Friend. If I played in a Deep Purple tribute band I may feel differently but you can't beat the Hammond Leslie combo for most stuff with the exception of the overdriven Marshalls that Lord used. The pedal also lets you get breakup at a tolerable sound level
If you haven't heard the tune, listen to the Hammond on Uriah Heep's Gypsy Live. Might change your mind a bit about how a trimmed out Hammond and Leslie(s) can sound. I believe Hensley used Leslies on that show and not Marshalls. I can hear them spinnin'.
H101
1955 Hammond RT3, HR40 & Leslie 251 wired as 147
1961 Hammond M101 (Thanks Chuck!)