Perpetuem and Sustained Energy are available at the checkpoints on most of the California double centuries and I've used them to ride thousands of trouble-free (nutrition wise) miles.
In my experience, they work very well (as does Hammer Gel), and I will continue to use them in the future. I'll occasionally use a bottle of Perpetuem (I prefer the Latte flavor) on 3 - 5 hour rides, but by far the majority of Hammer products are consumed on double centuries.
Regarding "real food" (as opposed to "funnel food" which is our slang for powdered drinks), I do eat some at the checkpoints, but they're a very small addition (guessing 10-15%) to the total calories from Perpetuem or Sustained Energy. Never had a problem mixing real food with funnel food on a ride.
I don't mix a thicker paste, but rather take small baggies of Perpetuem if I'm on a double where Hammer products are not supplied (Davis and Hemet come to mind).
Rick / OCRR