My thermalcouple is in the up pipe just before the turbo inlet.
I'm comfortable running up to about 1200 intermittently and I've hit 1250 a few times - I prefer to stay around 1100 though. I used similar numbers on the last setup and had 30-40k miles on the motor when I pulled it apart (damage due to overheating) and saw no evidence of damage caused by high exhaust temps. I'm also running 0.015" decked pistons with ceramic coating now so that should give a bit more wiggle room.
I only see that high of temps under full throttle pulling though, and only if I'm into it for a few minutes. Most of the time she'll run about 1000-1100 at 20 psi on hills and pulls well. I'm getting enough air to burn clean and keep temps down up until that last bit of fuel which is just about perfect. Could probably bump the wastegate up a bit and get lower full throttle egts, but maybe actually higher cylinder temps.
Cruising unloaded I'm running ~5 psi & 5-600* on the pryo.
I've got timing set pretty much right dead center on spec (luminosity).
The intercooler on my rig isn't fully setup yet, (air to water, water side isn't done yet) so I think that will help some. Even without it she behaves pretty well.
Under full throttle the coolant temps will creep up but not bad. My normal load is around 15k gcw and I'll usually be able to pull hills (cajon pass, I8 east from san diego, etc - max of 5-6%) at 50-60 with coolant temps up to about 210-215 and oil sump temps 10-20* higher. I took 2 heavy loads recently (20-21k gcw) up from san diego recently and with those I was down to 35-45 on the hills and saw coolant temps up to 225-230, but even then they took a while to get there. I'm running a 3 row aluminum radiator and some sort of a heavy duty stock fan clutch.