The misconception is that at speed, your rad fans are no longer the key factor in pulling air through the rad. This is not true. The phenomena that you witness when clicking your fans off was explained in my last post; there IS sufficient cooling from oncoming air, but NOT because it's rushing through the rad. A proper shroud will not cause a performance loss, even at speed.

If I had time to write up everything I had done, I would. Cliff notes are that there was an obvious and significant improvement in airflow through my I/C and rad after I added the shroud. Most of this testing was done between 100km/h and 160km/h (on a track, of course!).