i've used engine ice and water wetter + h2o on my bikes and get a 20 degree drop either way. But thats full replacement and the cons are that the water wetter has no freeze protection and the engine ice is $20 per 1/2 gallon. THe are also both very volatile temp wise too, sitting at a light i can watch the temp creep up and the fans kick on faster then with 50/50 antifreeze. But it also goes back down quicker once i get moving.
If you want you can try water + water wetter for the spring/summer and see but get it out before the first freeze or your gonna have problems (you could drain a little and add coolant but you'll loose most of the gains).