I've seen benchmarks indicating that the WBK-38 and the earlier FOP-38 are close to identical.
I recently replaced an Alpha PEP-66/Delta 38 HSF with a GlobalWin FOP/Sunon 42.5 cfm 80mm case fan HSF. My Slocketed P3E 600 @744 is now about 1C hotter than it was with the Alpha/Delta 38 combo.
After seven months of listening to a Delta 38, it's worth the extra 1C! Summer may change my mind about this, we'll see.