Hi,
now that I've learned a little bit about hinting and from l3thal's post, I guess the Steamboat map suffers from the same problem that I've with my own map (although not that distinctive since mine is really small). Q3A wasn't designed for outdoor maps and hint brushing an outdoor map like Steamboat simply isn't feasible.
Additionally, there are other performance "killers" like smoke and water. I guess you already tried to delete at least the smoke brushes? That'll give a HUGE performance boost. I accidently placed a single fog brush in my map once. Performance dropped immediately to 20-40 percent and I didn't change anything else.
Of course, you'll lose a lot of atmosphere and eye candy
...
If you guys are really planning to port the mod to another engine, it's suitability for outdoor maps should probably be considered.
Mapping gets more and more difficult the more you know about it
breli