I have never picked a stem length based on handling. It's always about my body as a machine, making it efficient, aero and comfortable. (Now, I am en ex-racer. Bike handling makes a big difference in how much I like a bike but very little in how I finish a race (most races; exceptions - criteriums, not my specialty at all and a few big time descents). And given how much time you are going to spend on your racing bike training, any differences in handling from stem length will make very little difference come a race. But a few percent power difference from that stem change - the difference will be huge.

I had custom bikes built that can use 120 and 130 stems but that is so I can stay with easily available stock stems. Other bikes have longer to much longer stems to get a good fit. They are bikes I would never race, but the stems are not the reason, not would they stop me if the rest of the bike was right.

My Peter Mooney, a bike that fits the C & V category well, now sports a 155 -20 degree custom quill. Looks great on the bike and much more important, the bike comes alive because I do.

Edit: re the hand position I set my bikes up for - I always set the bike up first to have a position in the drops I can ride all day if I have to. So if I have to spend the next 3 hours there going upwind, I can. If I am dragging my butt home, dead tired and stupid in the poor light at the end of the day, I can still ride those drops - meaning that rock I was too tired to notice won't knock my hands off the bars. Only after I get the drops dialed in do I finalize where the hood should be.

Ben