There's a lot of variables. For tropical reef fish, I doubt 85 F is likely to be a problem by itself, for example, but oxygenation can become an issue. Corals can be more touchy, and sudden spikes can cause problems, even if they are within the normal reef temperature range, which can be very extreme. I target 82 F as the base temperature, and I might see some beginnings of trouble at 86 F or so in some animals. Hard to say, though.
This article covers all the water parameters, including temperature, and gives some references:
http://www.reefkeeping.com/issues/2004-05/rhf/index.php