It depends on your personal preferences, and the type bow you are shooting, and the bowyer. Most of today's "high performance" longbows, especially the shorter ones, would be more accurately described as flatbows.

I draw 30.5", and in the longbow I like best I can shoot the 64" with no stack at all, but I prefer the 66"--it just feels better and is easier to shoot to me. Going as short as possible will give you more speed in a given design, but won't be as forgiving.

With the bows I am most familiar with (mild deflex/reflex ), I'd think a 60-62" longbow would be a good combination of speed and forgiveness, or a 58-60" flatbow.

Chad