First, just be sure to feed her plenty. She could still double clutch so you may consider some calcium supplement in her mice. As for temps, I would recommend the lower temps. I incubate my corn eggs around 79 (they literally sit on the shelf above the heat lamp on my display cage). It's been shown that they will hatch later at lower temps but it allows them to absorb more yolk. 84 is at the high end of the scale for corns and though they'll hatch sooner, they tend to have lower birth weight. With that many eggs, they'll have a lower birth weight to begin with so no reason to make it harder. I've never incubated higher than 81 and with the exception of her clutch of 42, my babies have always been 7-12 g. Like I mentioned before, the babies will probably be smaller so make sure to have tiny pinks on hand as you get closer to hatch date. It'll probably be between 65-70 days with the lower temps though I have had them go 72-73 days.