I led a winter ride series with a mixed group of geared, SS, and fixed bikes. All the bikes had brakes. I chose to ride SS on a geared bike. The rides went OK, but they weren't easy rides. In my case, we were all long-time friends so were willing to make allowances. Like waiting for the fixed riders to walk the 15% hills where the SS riders could cheat. Like not making the non-geared bikes pull at 24, though they had to be able to pedal 24 in the line. We had a Cat 2 come out with us on 60 mile rides. He'd quit and cut it short at about 35, plus occasionally screaming about "can we slow down a bit?"
Basically, if you want to compete with geared bikes and get their training effect, you have to ride geared. If you insist on riding fixed on other than solo rides, you aren't doing yourself or anyone else a favor. Personally, I wouldn't let you ride with us on our mixed rides for safety reasons. The only way to ride fixed safely in a line is to always have a positive pedal pressure and modulate speed with the front brake.
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