Well are you very lean at 170 or do you have a lot of muscle? You should fight at a weight you're comfortable at. There's no point in cutting unhealthy amounts of weight if you don't need to. I advise putting on some muscle if you don't have much now, see what weight you go up to and then decide. If you have to cut a lot to make 170 again, then don't do it.
Check here for some info on gaining weight:
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