It will not help your fish vs 84F.
Mine Bred repeatedly at 82-84.
Most plants will be fine, something to think about, the warmer the water, the less gas it can and will hold(CO2, O2 etc).
So less O2 will be present in the tank.
Don't be so anal about Discus, they breed and do well in planted tanks, perhaps you will not get a full 10" fish or 40 fry vs 20 fry, but that's the not the point, a nice tank with the fish you want is.
Food is more important to breeding IME than pH/KH/Temp.
Personal experience indicates that quality plant growth occurs at lower temperatures in the region of 72-80. My tanks get into the high 80s in the summer and plants suffer (more than fish). Growth rate at the elevated temperature is fast, but tends to be stringy and colours are not as good.