I feel the OP, I like challenges and generally don't enjoy over gearing content, so I did a experiment and only invited people +/-5 ilvl of the rewards. So a +10 I would only invite 910-920 ilvl. I did this 3 times and finished all 3 keys in time and had fun doing so because it wasn't a push over. Though I had to kick people out because they didn't think it's worth it gemming/enchanting your gear, so you always have to double check.