After upgrading my version of Crossover to 6.2.0 from 6.1.0, Steam starts up incredibly slowly (taking around 10 minutes for the GUI to appear) and HL2DM still starts up slowly. Once in the game, it runs extremely poorly - it's unplayable (less than 5 FPS, it seems, and the sound seemed a bit choppy). I am going to see if deleting the bottle and installing in a new one will help. I will post my experience here.
Well, I did it. I deleted the bottle and installed Steam anew, then downloaded HL2DM as usual. Steam seemed to start a bit more quickly, but HL2DM had a very long startup, which is no change. Once I got in the game and put in all my settings as I had them before (all of which worked fine in 6.1.0), I connected to a server that was running a map that I knew I'd never had any slowdown on. Additionally, I was the only one connected.
Unfortunately, it was quite bad. To start, it took a very long time to connect to the server (longer, it seemed to me, than before upgrading; I've had long connect times on every server I have tried). There were some graphical errors (visual clipping), the framerate was rather low, and the sound was definitely choppy. Intense actions, like an exploding oil can or death by a grenade, caused even further slowdown.
I would hate to play the game like this. It ran much better in 6.1.0; this is really a downgrade if anything.
Basically, reinstalling Steam seems to have helped its performance some, but HL2DM is still suffering.