I have several cone 10 glazes that I dropped to cone 6 with just 3-6% Gillespie Borate. It's worth testing. If you're firing gas, you can still fire reduction, and your fuel savings will be very noticeable. I've read that it takes approximately the same amount of gas to get up to cone 6 as it does to get from 6 to 10, and I believe it. It takes a crapload of fuel for the last 150F degrees creeping up to cone 10. That's a 50% savings!
A little off course, but no too bad. It's all related!