When I bought my bike, i THINK I bought a size(58) larger than I should have(56)
I'm doing well keeping up with fast paced rides(21-24mph), but I feel that I may be a bit stretched out.
My stem is a 110 with a 5 degree rise. The saddle is just a little higher than the bars, which is preventing me from getting into a more aero position. If I flip the stem, the reach will probably be too long.

The guy at the LBS(who I also ride with) said that I looked a little stretched out, and recommended that I go with a 90cm stem, and possibly flip it.

Let me tell you a bit about me first. I usually do a race training ride once per week, which range from between 35 and 55 miles. When in slower group rides, I've had a tendancy to straighten my left arm too much causing minor elbow pain. I think this is because I brake more on the slower rides.
Sometimes, I'll get some lower back pain. I have not raced yet, but plan on trying some races, but I probably won't do more than 5 per year.

Does it sound like I should flip the stem? go with someting shorter?
Maybe I should try the 100 instead of the 90. I don't want to go too short. I'm a little concerned as I'm 'dialed in' to what I have now. Maybe aero isn't that important? If I buy a stem, I'm going with a nice one, and don't want to throw my money around. A new stem would also save me 30-40grams.

Thanks,