Found this old but yet very useful article in SQL Server Magazine (InstantDoc 40925).
It is an in depth study of DBCC SQLPERF (WAITSTATS) with a lot of information on what to monitor.
There are a couple of interesting formulas in the article that came to my attention.
Initial Compiles(%) = (SQL Compilations/sec - SQL Recompilations/sec) / Batch Requests/sec
Plan Reuse (%) = (Batch Requests/sec - Initial Compiles/sec) / Batch Requests/sec
To determine the optimal Packet Size use the following formula:
Average Number of Bytes per packet = Bytes Total/sec / Packets/sec