My LBS's all have "fit stems" which you can put on your bike while on a trainer in their shop. Ride for a while, change angle and reach. You might be surprised at how obvious the sweet spot is.
Also, one of the LBS's (at least) has a whole rack of take off stems that they let you use for a while to test, assuming you ultimately buy one from them.
If you're the guy who's LBS says you can't use non-Deda stems w/ Deda bars, find another shop, preferably with both of the above ways of deciding stem length and angle.