I rode quite a few 10 milers fixed in the 1990's, riding fixed was good because you just focus on riding as fast as you can (yes i know it sounds obvious...)
With gears i find i change up to too big a gear only to have to change back down 30 seconds later
My fastest TT was on a geared bike though in late season, only used the fixie early season, first 4-5 TT's
I rode quite a few 10 milers fixed in the 1990's, riding fixed was good because you just focus on riding as fast as you can (yes i know it sounds obvious...)
With gears i find i change up to too big a gear only to have to change back down 30 seconds later
My fastest TT was on a geared bike though in late season, only used the fixie early season, first 4-5 TT's
HTH
thebaldbuzzard