Have done a lot of harness work -- and been through the debates on this.....
For some the GPT is perfectly fine except in the engine compartment, others won't use anything except SXL and the other higher temp rated types regardless. Seems everyone has their own reasons or claims.
This link (and actually this whole little site) is helpful, short, easy to digest and might help you to make up your own mind:
MKII, PDW, Torsen 3.55 Pin Drive IRS, Dart 393W, AFR 185's, Victor Jr., Accufab TB, Accel DFI GEN 7 EMS, TKO 600 wMcleod Scatter&Street Twin Clutch, 1+1 Elec., TTD's, Da Bat Paint