The ATI dampers do make some extra HP on an ARCA type 840 plus HP unit--at least on my friends dyno--he has seen up to 15HP on back to back test.
Fluid styles have been out of favor for a long time now in high end race units. They have several problems--they leak ( or Will leak) , the fluid turns to glue and they quit working and often cause other problems when that donut quits rotating in there, and..a rock or a slip with the wrench, you get a very small ding and there! It is now worthless way before it leaked or the fluid jelled. Look at how stock style dampers have NONE of those issues and I can't see any reason to ever use a Fluid style damper.
You just can't beat a high quality stock style damper unless you go to the ATI--The ATI's often require honing to fit as cranks these days are all over the place and...they make many hub styles that often will not work with Indy front covers, etc etc--Do your home work before buying one--they make a ton of different units for Mopar.
Pioneer stock replacement is a winner if you do not need SFI. The Aussie dampers from PRO come SFI or stock and are killer units for very reasonable