Maybe I missed it but I did not see anything on performance. Of course I doubt MySQL is in the same league as MS SQL. I think MS SQL like's to compare it self with Oracle. And of course others have suggested comparing Postgres. But I think you will discover the lack of many of the features in Postgres too. But I think performance may be a better match to MS SQL and all the important features (triggers, SP's, etc) will allow comparing. BTW I found MySQL to be the second fastest database engine - just behind FOX.
John