In all honesty and without beating around the bush, the Festool vacuums aren't very good for drywall. Even the AC versions. I have 2 of the AC vacs tried both with bag and with auto-clean several times. Ive resorted to using an Ultimate Dust Deputy on top.
If you use a bag the fine drywall dust completely cakes up the pores in the bag resulting in dramatic loss of suction after a short while.
That is why they came out with the autoclean, which can be used without a bag or with an open liner.
Unfortunately because only a single filter is used in the vacuum, each time the airflow is revesed to blow the dust out of the filter you have a loss of suction. In practise that means you have small puffs of dust at your sander or grinder each time the cleaning functions kicks in.
Bottom line if you want to sand a lot of drywall, use an AC vac without fleece bag and/or a cyclone pre separator. And if thats the primary use of that vacuum look at other manufacturers. The Metabo ASR 35 for example is a significantly better performer for concrete and drywall dust compared to the Festool auto clean vacuums.
And now for a little rant: I dont get this obsession with HEPA vacs. For some reason the people in the States seem to associate HEPA = good and clean air, non HEPA = bad vacuum. Unless you have money to burn, you should never use your HEPA filter without a pre-filter. Be it a bag or something else. Because of the materials used and the density of a Hepa filter it will clog up in no time. By blowing it out or cleaning it, the filter will be damaged and lose its HEPA rated filtration.
Thats just one of the reasons just about evey manufacturer has developed special synthetic filters to be used with their autoclean vacuums. And most of those, including Festools synthetic autoclean filters arent HEPA rated.
In any case, the best of luck with your purchase whatever it ends up being.
