SmokeaJoint
Bluelighter
IMO, the biggest risk is what happens if you take a large enough dose of barbs, and the stims wear off first. Same as what happens to peeps who mix H with stims, then end up dropping too low (a BL member recently died from this). As far as the drugs themselves, googling "barbiturates with stimulants" and such would likely turn up some references.
Google only turned up things like "Are barbuturates a stimulant?" and the like. Dumb fucking question btw. And as far as dosage goes, I haven't taken >50 mg of the Seconals, ever. 50 mg was plenty too, and they come in 100 mg capsules.
Something a tad worrying that popped up, alot of celeberity barbiturate related deaths had cocaine also with them. From what I gather though, its like what you said. They went overboard on the barbs, and the stims ran out, and breathing stopped. However, if 50 mg doesn't do anything in an hour, I WILL NOT redose. On either the stims or the barbs. I'm not big on life, but I don't feel like dying this week either.