A little update in case anyone with a similar setup/problem as me is contemplating a Corsair H80. I bought one and fitted it and saw a drop of 30c on full load temps and around 27c on idle temps. The back plate for the cooler also fits over the heat sink on the bottom of the motherboard without any problems. One thing to note though is the H80 only just fitted in my case! It would not fit on the rear exhaust slot because the slot was too close to the power supply. Instead I removed the HDD rack (which is removable anyway) and put the H80 rad and fans on the front intake slot. This wasn’t too much of a problem for me because I only have one HDD and it fits in a bay under the floppy drive slot. The temps above were taken with the H80 in the intake slot.
Thanks to everyone who had previously helped me with this issue, it seems like the CPU cooler was the problem all along.
Thanks to everyone who had previously helped me with this issue, it seems like the CPU cooler was the problem all along.