When I did the math for the Gilson impellers they rotated at about 1000 RPM with the engine at 36000 RPM depending on the model. The worm drives are 21 tooth, double helix for a 10.5:1 ratio and yield an auger speed around 95 RPM.
Can they go faster? I think it certainly depends on the worm drive in question. An oil bath case running the worm in tapered needle bearings probably has a lot of headroom. A grease packed case relying on Oilite all around, not so much.
The raw speed, heat and wear are one thing. A bigger concern is probably the higher force/shock loads it will be exposed to when you spin it up. The lesser cases have a hard time staying together as it is.