Cooool map

Yes, snow in mid-day with sun shining on is blindingly white, so it makes sense, though it's harder to play on...
As for the mapinfo file: have a look at ~/.nexuiz/Docs/mapping.txt
Balancing a map (looks <> performance) is a pain in the ***, from my experience it's trial and error. It helps to make a demo and run timedemo after changes to see how it influences average performance.
Basically, triangles and high quality textures are not too bad, but detailed models with spawnflags 2 and 4 can cause quite a performace drop (it's better to leave them non-solid and put simple clip brushes over them). Shaders can have great influence, as well as deluxe map effects (bump/norm).