Can I optimise search by increasing hot buckets?

Three questions in one.

1. Are hot buckets faster than warm for search.
2. If so is it because they are in memory or because the file is already open?
3. Is it a good idea to have 30+ hot buckets to speed up data access?

For background, we are indexing 100GB/day and searches over a few hours seem slow so looking for ways to optimise.