I was curious about scaling between Q3 and D3 and I realised that because they had different player character sizes the scaling factor involved would need to be based on the relative sizes of the collision boxes.
Q3 boxes are 56 units tall.
D3 boxes are 74 units tall.
74/56 = 1.321428571
This can be used to make D3's physics a lot more similar to Q3's. Q3's standard movement speed is 320units, multiplying this by the scaling factor results in 422.85 (round up to 423). This can be achieved with the following commands in Doom3...
This doesn't just apply to single player mode, this could be used to run a D3 multiplayer server too.
Jumping still needs a bit of work using pm_jumpheight and whatever the gravity command is, but I've not figured that one out yet.