Currently using AI ovens. 3.2cf have been my favorite overall.
I recommend staging your oven in increments of -5. (Ex: -5, -10, -15) pull vac slowly while doing this. I let it sit on each increment for at least 5min. For the final stages I will pull a slow vac from -25 till I reach -27inhg. I will let this stage sit for 10-15min before pulling the final stage. I let that stage for another 10-15min with vac valve wide open. I flip every 24hrs and keep doing this for 5-7 days. Have had great results and consistently sitting under 20ppm Butane. Hope this helps!