It's such a new car that I think anyone who starts to modify it won't have any other cars to compare against, your literally going to be one of the first!
Although I think mods which you can do to the TDCi 115 and 130 will be applicable to the ST TDCi, and you'll see greater benefits.
As for reliablity, your guess is as good as mine.
mine is "custom" remapped stage 1
hp doesn't interest me
it's torque that get's you somewhere
so they took the limiter of the three 1st gears and got some grunt out of it
with new turbo on it (stage 2) we will remap it again and hope to get over 500nm then (and +/-200hp)