EGT is the critical and limiting factor for 300 Tdi performance "upgrades".... the CH is made from an alloy which, reportedly anneals at 720 C. .... So, you'll need a good, accurate EGT gauge....
I know someone who ran a 300Tdi at 200HP output - it was fine and dandy until he melted the CH with too much fuel ( I.E. too much fuel for too long ).
I'm running an enhanced 300Tdi, coming up on 140K - last 40K at 145Hp output.... fully synth oil, and maintained fastidiously ....
More power is available, but IME, the intake roar is intolerable...
Also, can you insure the thing with such mods ? I had some issues in this regard, so ....