The varchar issue only applies to varchars that are defined with a field length of 254 and above. SCR treats them as "memo" fields when they get to that size, and little can be done with them in formulas.
Because SQL Server allows easy development and deployment of stored procedures, and SCR supports the use of parameters with stored procs, you can achieve excellent performance (limited only by your own SQL coding abilities - no one to blame anymore!).
You'll need the professional or developers edition of SCR to access SQL Server. Good luck. Malcolm