Hi,
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As for Repel, I don't think that you still can encounter higher level pokés in PRO whilst active. Besides, I don't think the rare pokés spawn at higher levels. Actually, it's even more often the opposite, at least that's the feeling I have (especially Charmander in Cinnabar Mansion, iirc)
But I only used 2 or 3 repels in 1300 hours, so... xD
You can still encounter level 50 plus I think