I am assuming you have read
R_speeds the tutorial?
I haven't replied because Kol is doing really well answering the questions
But for what it's worth, large caverns with lot's of textured brushes and lot's of space will increase compile times. Null anything the player can not see, but is actually in the visible part of the map. (Like if you noclipped around inside.... I am talking about the brushes you would see then, not the external brushes)
Also, when running r_speeds 1, you will only get a true representation when you do a full CSG,BSP,VIS and RAD compile. Failure to use all the compile tools will
NOT give you a true indication of the speeds.
As for Hint Brushes... I tried to write a tutorial, but kept getting results that were not consistant and didn't follow any pattern. So rather than write about something that I couldn't figure out but have had a little success with, I decided not to do it at all. Hint brushes can increase the wpoly count if you are not careful.
I have found that the best way to manage speed is to build the map with them in mind in the first place. The addition of a few enlarged textures, a few func_walls and a few solid brushes to block the visible line of sight works wonders. Plan before you map ! Don't forget that the engine will think you can see over walls, so walls to block visibility in caverns are not always good.
Also, for those who tell you that a 13 Hour compile time is acceptable... they are full of it. There is no reason that a map should take more than an hour on a PII 400Mhz with 256Mb of RAM...... Actually that isn't quite true as there are some designer specific maps, but it is a good general rule. Case in point was an RMF that I tried to compile recently, 5 hours later it was still going. A little fixing reduce the compile to 15Min's....
Moral of the story.... If it is taking a long time, have a look at the rmf from the engines point of view and try to see why.