The easiest way I've found to increase boot speed and application load even under heavy system load is to use the pf kernel patchset. With a properly configured kernel using BFS, BFQ, and LZMA compression, my system is amazingly fast. Even when compiling and both cores at my laptop are at 100% my system is fully usable. If you have a Macbook Pro my kernel configs are here: https://github.com/meinhimmel/kernel-configs