Performance page
In my highly scientific, mathematically rigorous benchmark of PyMySQL vs MySQLdb on CPython 2.6, Ubuntu 10.04 via VirtualBox, I ran the MySQLdb test cases ten times for each module. The average time for MySQLdb was 2.2258 seconds, and for PyMySQL was 2.3122. The very firm and reliable conclusion that can be made by this double-blind exhaustive study is that PyMySQL is approximately as fast as MySQLdb.
Okay now, in all seriousness, it seems that PyMySQL is in the same ballpark as MySQLdb, but we have not focused on performance yet.
My guess is that the packing/unpacking of the binary protocol is a tad faster in the 'C' implementation of MySQLdb. But, you already knew that, and were looking for a Pure Python solution, this is it, and the performance hit isn't big enough to worry about.
To run the full SQLAlchemy test suite on a given machine, MySQLdb takes 298 seconds and PyMySQL 306. Pretty good, really.