If you want Snort to go fast (like keep up with a 1000 Mbps connection), you need to use unified logging and a unified log reader such as barnyard. This allows Snort to log alerts in a binary form as fast as possible while another program performs the slow actions, such as writing to a database.
If you want a text file that's easily parsed, but still somewhat fast, try using binary logging with the ``fast'' output mechanism.
This will log packets in tcpdump format and produce minimal alerts. For example:
./snort -b -A fast -c snort.conf