Ok, on a whim I purchased some Perpeteum made by Hammer nutrition. I have to give it top marks, and I do not want to promote any particular product. But this stuff works well for me. As we all know, individuals are different and my results won't be the same as yours.
EDIT: Most of my rides are just a few hours max, 2-3 AVG. I never ride 8 hours anymore. I like Perpeteum for my length rides.
Here is the scoop. I have been making my own energy bars for years. They work well and prevent bonk fairly well, plus they taste good. So, I was not wanting to pay for supplements. However, Gu, Clif Blocks, jelly beans and the like do work for me on longer rides. I sometimes use Gatoraid and tried Cytomax. All work well for a boost.
But the Perpeteum stuff simply works better. The end result is a couple of tenths more speed over a long ride. Plus I simply feel better. In my case, I have found the secret!
Cytomax claims to have lactic acid reducers and I suppose they work, but Perpeteum works better. Not sure about the lactic acid, I generally don't have a problem with burn. However Perpeteum results in stronger feeling legs during a ride, and especially towards the end the day, after my ride.