Yeah look, I'm a metal guy at heart, love my ib7, an 8 string is pushing it, but a 9 is just stupid. I'll try to find the rob Chapman vid where he demoes a schecter 7, 8 and 9.
Early 8's were 27", but even then the string tension was a bit loose. Ibanez are 28-30 now, as is esp. Consensus is 28" for standard but if your planning to drop tune, 30". Personally I'd go 30".