There isn't a need to go above 600mg/day KSM-66 (30mg/day withanolides), but the highest dose I've seen used in a study was 100mg/day withanolides (from 1000mg/day Sensoril) that noted improved reaction time (cognitive and psychomotor performance) after 14 days of supplementation.No need to high dose it. 300 mg twice daily is good enough. I notice the benefits around week two or three. Not saying it doesn't work prior to then, but that is when I start "feeling" it. By that I mean my head is less foggy on a daily basis, I wake up more rested and I just feel better overall. Here are some good reads.
http://www.ergo-log.com/ashwagandha-strength-lean-body-mass-fat-percentage.html
http://www.ergo-log.com/human-study-ashwagandha-boosts-testosterone-level.html
600mg/day of a 5% withanolide extract is a staple of mine (either from Jarrow or AlphaMax XT). Sometimes I do like to take a bit more though, which will often just be another 300mg with the PM serving of AlphaMax XT, giving me 300mg AM and 600mg PM.