Originally Posted by Michael Cox
And that is why I threw out the question. So if you are using a shroud of say 25-38mm which we all agree has performance gains such as better air flow across the fins. Then I would think it's possible that a fan with more CFM may have an advantage over the fan with more SP in this instance.
No. The higher sp fan will always be better able to push air through a heat sink or radiator. If you are looking for reasonably priced high sp fans, besides SanAce (SanyoDenki) you should consider Panaflo, NMB (same thing really), EBM Pabst, Sunon, Delta, Rotron, etc. Basically these are all 'server' fans - they are not pretty to look at, they don't have led's and fancy names. What they do have is solid dependable performance for your money.
The testing that was linked in earlier response, done by Martin, is the best reference you will find for fan performance of commonly used 25mm thick fans.