Good question, let's talk about it!
With the turbo there is more heat input on the system but so far I have not noticed any issues with any of the cooling systems on the trucks that we have turbo'd. With that being said, I do recommend the cooling system be up to date and in good working order on any truck that is being turbo'd. Also the ambient temp under hood will be hotter after cruising and pushing hard with the turbo so anything on the exhaust side like aftermarket electrical may need to be wrapped in higher temp loom/shielding if it's anywhere close to the JPipe/turbo. The insulation we provide cuts the heat down a ton but there is still heat radiating off of the pipes.
On the topic of actual water temps.... The test mules radiator is a TYC that is 4 years old with a 4 year old modified blue hub fan clutch and it runs exactly the same as it did before. It has always lived right at 195 on the highway when cruising and in town and continues to do so. The highest temp to date I've seen on the test mule was 208 degrees going over Berthoud Pass (11,300 ft) on a 95 degree afternoon loaded down for a weekend of camping just absolutely flogging it. Still well within the safe working limits of the 1FZ. Last summer we took a road trip to Oklahoma City when it was 90-100 the entire week and humid. Stayed around 198 the entire time with the AC on high everywhere we went. Took a clients turbo truck on its first true maiden voyage this weekend from Denver to Walden CO for some camping to put miles on the new engine rebuild and one of the obstacles is Cameron Pass (10,300 Ft). On this 80 we installed a temp gauge into the upper radiator hose neck in the boss Toyota so nicely gave us. Max water temp pushing fairly hard was 193, yesterday it was in the mid 80's. This truck is on 37" toyo mt's with trail gear bead locks and fully armored with a roof top tent... heavy but it had no problems.
@baldilocks if you're going to Rubithon I think this one will be there. On Rosie we've had no issues highway cruising, haven't gotten it into the mountains yet but I don't think it's going to have any problems. Trail cruising haven't seen anything different, turbo vs non turbo. Offroad you are almost never loading it to the point to where you'll build any boost so there isn't much added heat to the system.
I do recommend people change with their driving habits a little bit and the main thing is don't shut it down right away after flogging it unless necessary. Give the fan a chance to pump some of the heat out after long drives, long hills or hard pulls. After cruising at 75 for hours on the highway I'll tone it back the last few miles coming into town where I am going to fill up and let some heat get pumped out. Doing this also gives the turbo a chance to cool down. The center cartridge of the turbo gets extremely hot and a few minutes of coolant circulating with little to no load will bring it's temp way down. No need to go crazy with the time but if you can give it 2-5 minutes of little to no load that is probably enough to shed a lot of the built up heat.
I have a road trip this upcoming weekend from Denver to the little belt mountains in Montana, over to Bozeman, Jackson and back to Denver with two turbo trucks. I'll get some good data to post up. Looks like it'll be 80's.