Good topic. Good discussion here too though some of it isn't so much about handling as about general fit.

I've found the the difference in handling from one drop bar bike to another is nowhere near as great as between drop bar and upright. I have a hard time riding an upright in a straight line! That being said, I do think moving the hands forward with a longer stem makes a difference, just not a very big difference.

I pick the stem to match or compensate for the TT, but I just guess, no multiple iterations involved. Then if the bar was too close I've lowered the bar (literally, and figuratively too I guess) to where my body position feels good. I tend to ride on the hoods most of the time. I've never agreed with any line-up-the-skewer rule. Every bike feels different and the shorter frame(s) feel smaller for the first half mile. After that they all feel comfortable.