Have (had) you considered using a TLC5940? The 18V is a bit above the maximum but I suspect that would not be a problem.
I am wanting to put a few models together, with between 2 and 6 servos. For the 2, 3 & 4 servo models, I was actually thinking an attiny85 hooked up to the 328P main mcu via I2C could be used as a PWM source. I'll have both ICs so experimenting is on the horizon. Do the TLCs have advantages over the use of another mcu?
Oh hmm. Are you driving the devices directly from the TLC?
The attiny would need FETs or something to drive the servos.