If you generally know what you are looking for ahead of time, one method is to keep a process always running that tails a log file. This process can then send everything it finds to another file, which can be searched instead.
in reply to Re^2: Matching lines in 2+ GB logfiles.
in thread Matching lines in 2+ GB logfiles.
If you need to beat grep, you can, but you have to do things that grep can't. This includes knowing how the files are laid out on disk (esp RAID), and how many CPUs you can take advantage of (i.e. lower transparency to raise performance). You can write a multithreaded (or multiprocess) script that will read through the file at specific offsets in parallel. This may require lots of tweaking though (e.g. performance depends on how the filesystem prefetches data, and what the optimum read size is for your RAID). FWIW, you may want to look around for a multithreaded grep.