Max water temperature for wetsuit swim?

I have done a pool swim (81 degrees) in a wetsuit as a trial run right after I bought it.  After a 1000 yds I was totally pooped from the heat (it was a full sleeve wetsuit). 

78 isn't bad for a sleeveless.  75 is better. 

Well, USAT sets 78 as its cut-off water temp for wetsuits, and that's a pretty good guidleine.  I have used a fullsuit in warmer water to no ill effects, although when i have ventured into a 80-something degree pool to test a couple of suits, it's been unpleasantly sauna-ish.

You'll be fine in mid-70s in a sleevelss, and the more you swim in it before B2B, the better it will be for you.  That said, sleeveless models require less adjusting-to, simply because there is virtually no risk of having constricted arm movement.  However, you might still have to get accustomed to potential tightness around your chest, although Xterra suits are very pliant and pose less problems in that regard than do other models.  And if you are a heavy kicker, a wetsuit will initially throw off your mechanics.  I say do EVERY swim between now and B2B in the wetsuit!

And remember to FULLY BodyGlide your neck, to prevent chafing.  Don't scrimp!!!

USAT sets the limit at 78° because people tend to have heat strokes and die when wearing wetsuits above that temp.  Will you have a heat stroke if wearing a wetsuit at 79-80 probably not, but the chances go up considerably. If you wear one at 85° you might want to make sure your will is in place.

I think they should drop that temp down to 75° which would be much more reasonably.

OK, I don't know the ITU - USAT relation, but ITU sets max according to distance/cut off swim time. For AGs: 22C up to 1500m, 23C for up to 3000m and 24C for up to 4000m. That's 72F on the short distances.

I did a test 1650 yd swim in my local pool with my sleeveless with a water temp of 85F.  I did not die.  I did get warm though and got out of it as soon as I finished.  One tip is to have cold water in a bottle nearby for drinking.  I tend to get hot after a hard set in much the same way.

My race had an official temp of 77F, just barely legal.  I had no heat issues whatsoever.  Came out of the water 2nd in my age group.  

I am about 180 and 5'10", 43 years old, swam year round as a kid, and swam that 1650 in 23:30.  Again it was warm enough to feel like I was sitting in a hot tub, but I never got faint or felt lightheaded.  I did ask the lifeguard to keep a close eye on me just in case.  I think under 80 is ok, 80 to 85 starts to get sketchy, and much over 85 is too hot regardless of wetsuits.