Obviously, the hotter it is, the quicker it will remove them. You just have to balance the cost of a few extra seconds for your employees to spend on them (if it is cooler) vs. the increase in cost of utilities to heat the water (if it is hotter). Also consider if time is a factor, and if you really need to remove them as quickly as possible due to volume demands and not being able to let the chemical dwell, or if that bit of extra time does not matter.
I know a lot of operators who use a good bug chemical and use cold water for hp guns. If your chemical is good and you can let it dwell long enough, heating the water may be overkill.
Generally, presoak shouldn't be heated over 115 or so - might be a good rule of thumb to keep that as your upper limit for your hp guns too.