Well 1 year later and I've given my system a good cleaning out, the dust behind the fans pulling air into the rads was quite bad. All cleaned now and good to go again.
I checked my temps with all my fans running at 900RPM and my GPUs were idling in Windows at about 34 degrees, before cleaning.
I cleaned the dust out (which took me about an hour in total)
I tested my system by turning off all my fans, it was idling in windows with the GPUs sat at 53 degrees. I know this is fairly high. I turned the fans back on just on my top rad with the 8 fans, at around 7v (so around 900RPM) and my temps dropped to 38 degrees.
Lastly I turned on the bottom fans on my two rads and the temps then dropped to 28 degrees, shows just how much a good clean out gives your PC.