Having just installed the screw drive this weekend, I don’t have enough data to personally tell you how it’s working.
That said, the screw drive upgrade comes with thicker, rigid side plates and risers. Kind of makes the stock ones look hilarious when you do a side-by-side. These plates also have two additional V-wheels, for a total of six. That definitely improves the rigidity of the machine.
The real difference from the screw drive though seems to be in motion. Previously, when working on furniture-size stuff with a lot of pieces, I really tried to push the feed rate. Especially with 3D carves, the difference between being able to run at 120 IPM instead of 60 IPM completely changed how much I could get done in a day.
So I pushed my machine with belts, and generally things would be fine. But then I’d run into some issue and end up having to trash a work piece. Sometimes the X-axis belt would slip while in motion. Other times, I wasn’t delicate enough about a tool change and the gantry would slip. In the end, I had to change my process to go back to a lower feed rate and to minimize tool changes, which sucks.
With the screw drive, the holding torque is high enough that there is no way I can make it slip during a tool change. I’m also excited to be able to do more work in aluminum now rather than just wood, which I was always worried about with belts.