No personal experience (I tried to grow mine out not long ago, and couldn't make it past chin length before it started driving me nuts!) - but I wonder if you might find inspiration here. The author appears to have long hair, and usually does 2 braids. Might be worth asking her opinion directly, as she does lots of long distance riding. Her blog is pretty amazing reading btw - lots of inspiration there
Good luck! Cut if if you want to - but I'm confident you can find some kind of solution if you don't want to.
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