Actually, Marc, I don't think I've every seen a Double Bonus game with such a pitiful paytable (8/5). They're usually 9/6. There are Double Double machines with 8/5, though, and that's not good, either.
There is indeed 8/5 DB out there (in fact I have even seen 7/5). It's pretty ubiquitous at the .05 level, but I'm sure you can find it at the .25 level in the bigger Strip places.
Haven't seen any 8/5 or 7/5 DB. What I have seen is a lot of 9/6/4 where they short the straight from 5 to 4, that lowers the payback to around 96%. Lower than that is truly bad