Pre-Turbo is considered more accurate since a great amount of cooling can happen between the manifolds and the DP. The cooling is not linear so it's not as effective in determining egt's.
Pre-Turbo was VERY simple and took all of 30 min to drill, tap, mod, and wire up. I've never done post turbo install, so I can't comment about that.
1250* F is the maximum SUSTAINED EGT you want - you can run all day at or below that temperature. Short spurts (track/truck pulls) you can reach as high as 1300-1400 with no ill effects - then again you need to think about how your motor costs 10k to replace!