Thanks guys, good advice. Makes sense to have 140mm pushing more air at a lower speed. Yes Kraco, the case can take that size. I always planned to replace the stock case fans regardless.

So I want to blow in more air than is exhausted? Makes sense again. The reason I wanted the top exhaust in addition to rear is that my CPU heatsink will be very close to the roof of the case (just below where the top fan sits) so it seemed right to me to have something there directly above it to draw air, as well as behind it.

Noctua and Scythe are also my favoured brands, they're also quite expensive. In this particular instance someone recommended Nexus but I've never used them. It's probably worth it to put more money into this just for that guaranteed quality.

So with the temperature sensor, take the CPU for example, does it actually sit in-between the CPU and heatsink, or just near it? Never done it before, hence the reason for researching how to do it properly.