What kind of trigger pull could someone expect if they ran a NY2 spring with a 3.5 disconnector?  I'm looking for something that will make some type of improvement on the stock NY2/5# disco combination.

That depends on what you mean by improvement.  If you want to get rid of the long hard pull of the trigger, get rid of the new york trigger spring entirely and put a stock spring in it.  If you just want to reduce the release point, or click of the trigger, go ahead and put a #3.5 in it.

I have a NY #8 and #3.5 in one of my guns, and I can't say that I hate it.  but the standard trigger spring, and a #3.5 or a #5 connector feel much better.  To be honest with you, the actual let off between the #3.5 and the #5 connectors feels the same to me, the #3,5 just feels more mushy.

The NY triggers are simply designed to give you a double action revolver feel to the trigger.  So all the take up before the connector trips is harder.