n57h - Here's another spin on your question. I run a market data analysis company for investors, and we track a great deal of multifamily information including cap rates in a number of markets.
In our database, the average multifamily cap rate for Class A properties is 5.5, Class B 6.6, and Class C 7.5. The range is impressive though - for Class A properties the range is from a low of 3 to a high of 7.8. You'll need to drill down into your markets of interest to find the real numbers.
Make sure you're calculating and using caps based on actual data and not proforma.
Finally, a great book written by a former bank financial analyst that will help with the evaluation of MF projects is " The Complete Guide to Buying and Selling Apartment Buildings" by Steve Berges. He has a great, long chapter in there on financial analysis, and while you won't have your MBA when you're done reading this one, you'll understand the basic metrics.
Have fun- Mark