Easily seven to ten days, no psychosis any of the dozen + times I did this - close friends have repeatedly verified I was always coherent and papered pretty normal if talkative but never any inappropriate/psychotic/paranoid behavior. Never paranoid. I was using very clean glass from Tucson in 2002 - 04 when I did this - 8 ball would last me three days during these runs. I've also managed 36 - 48 hours of driving without more than a piss break on phentermine (huge amounts - like 1000-mg over 24 hours). No shit.
Most emotionally "off" I got was mild hallucinations and depersonalization - only with meth - phentermine just left me tired and depressed and short of temper, and of course severe hunger (with both prolonged meth and phentermine use).
After the seven to ten days w/ meth I usually ended up falling asleep with a hot pipe in my hand sometimes after a handful of benzos or opies, sometimes just the meth had a paradoxical effect after so much use. Always passed out cold for 36 - 48 hours. Showered, ate, drank water, took vitamins and spent a few hours sober. Then repeated. Did this for about two years. Then switched to BTH to get off the meth w/o going into a somnolent stage of deep depression. The H kept me awake enough to eat and not become depressed. This habit was running me $50k/year.
Never doing this again. I've heard the stories of people staying awake for two - three weeks. I believe this is possible although not without some HR elements applied (eating, resting if not sleeping, lots of hydration and a solid mind and body going into the experience.) I always outlasted anyone around me, most went a little nuts around day 4 -5 and I sent them to sleep b/f they affected me.
Not trying to one up anyone but, yeah, a week was easy enough for me with very clean, pure glass. Smoked, hot railed, insulfated but not injected. IV sessions couldn't run more than two days for me - too intense.
I actually have fairly good memories of those times, I got to spend much more time with close, non-judgmental friends than I would have otherwise, and went out almost nightly (until maybe day five - then I tended to only go out during the day to avoid DUI checks and such or to score again.
The eventual toll it took on my body and my moving back to heroin after the two year run was ok at first but that turned into my biggest beast to beat to date. A decade later I'm still taking bupe.
But I am free of all non-prescribed meds, only taking very legit prescribed meds, and my life is much better. The chaos of meth use is hard to manage unless one has an a very pure, readily available supply and even at that two years burned me out and I needed a break. I bet in that two years I slept less than I have the last three months of this year.