Straight of their tech sheet on their website:
Cooling System Fluid Stabilized Temperature
50% Glycol/ 50% Water 228°F
50/50 with WaterWetter® 220°F
Water 220°F
Water with WaterWetter® 202°F
Those results were done with a iron block 350 Chevrolet with aluminum heads run at 7200 RPM for three hours.
Water Wetter is basically just like a spoon full of detergent. It breaks the surface tension so there's less air pockets inside the engine. Although if you own a race car it's nice since it evaporates instead of leaving a slick spot on the track like regular glycol.
I'm not seeing a point in lowering such a low compression engine, which doesn't have a problem cooling, a few degrees. As the guy that has to fix broken bikes all day, I always use the "Don't mess with it unless there's a reason" mentality.
If you feel the need to tinker, the radiator cap is on the right hand radiator under the cowl of course.
See part #3:
http://www.bikebandit.com/oem-parts/2014-honda-gold-wing-valkyrie-gl1800c/o/m156350#sch846738