Just had a quick re-read of pHaestus' WC tips, I remembered he had linked to a good article on shrouds.
http://www.nmbtc.com/pdf/forum/engineering_101.pdf
So if I understand this right, I need to keep a certain amount of space on both sides clear.
From reading various threads here I get the impression that pulling through a rad is better than pushing air into one. The rad is going to be placeed right at front of the 5.25" bays on my case.
Depth in brackets
fresh air (casefront wall) |> RAD(1"/25mm) >shroud(1"/25mm)>Fan(1"/25m)>Shroud(1"/25mm)
So the fan is sucking air through the rad from the outside, and its got a 1" shroud on both sides.
This takes up roughly 4"/10cm from the front of the case, leaving another 8-10cm behind for me to mount two cylinder shaped reservoirs (6cm diameter.) Hopefully these won't mess with the airflow too much.