PushPull Vs Single Fan

[Cru54d3r]

How much better is a push-pull config than a single fan?

I had never really considered mounting a second fan on my setup (thermalright ultra 90 with 56cfm 92mm fan) as I always just assumed given the proximity of the rear exhaust fan that it would be a bit overkill having 2 fans (the pull and exhaust) so close together - is this not an issue?

Can any one advise as to the temp drops they saw?

Thanks

 

[Cru54d3r]

so perhaps if the pull fan had some sort of sheath or something made (chimney-like) to direct the hot air upwards (perhaps to a top fan) then the whole system would work better (allowing the exhaust fan to remove case/rising gpu heat) ?