I can only give you my experience. I tried to use that setup to separate my 20 acre pasture into two 10 acre sections. It worked well for a while, but if you are using a low impedence solar charger like I was, it does great on noses, but doesn't provide enough oomph to get through their winter coat too well. Mine got in a habit of leaning over the short step-in posts to eat the grass on the other side - once they start doing that they lose respect for the fence and it's all over. At that point they start getting tangled, bolt, drag your tape all over the county, break and bend the posts, etc. Overall, not too great.
However, as your horses are small, the height shouldn't be any problem, and you are only looking at 6 months - without a winter coat - so you may be OK. If you go that route, be sure to lead them up to the fence and make them get their little noses zapped a couple of times. They just hate that...
