RTC index and worked just fine. Front derailleurs at that time, the SRAM mechs were not great. I’ve run shimano and campy front mechs with sram shifters to good effect. Have not tested every combination and this was 10s days so not that useful today as folks go to 11 and 12s.
FWIW, I swapped out mechanical for first gen Di2 as soon as there were TT shifters for Di2. That was not as easy at the time as there were no internal batteries and no holes in frames for cable routing. Solved the battery issue and drilled holes in frames to hide wires.
Di2 electric was magic on the TT bike. Could shift under load and from both the extensions and the cowhorns which is more useful than it might first appear. Particularly on technical TT courses.
I recently grabbed a SRAM wireless 11s group on closeout pricing (am cheap) and plan to convert my Shiv to wireless 11s. Didn’t go 12 as for the courses we ride 2x11 is more than fine.
TL/DR - If funds aren’t an issue, I wouldn’t mess with mechanical or Di2 for TT bikes any longer. Just do wireless and save a lot of hassle routing wires and hiding batteries.