I'm not the engine builder on our team - but I can probably at least partially field this question.
We used them to get adjustable rockers. We are running Comp Cam's
'Pro Magnum' lifters which have less compression in them - so we can run much higher RPM's without getting slop in the valvetrain. IIRC they only pump up about .005 - no way you can run them without some manner of adjustable rocker. As it was, we ended up running .050 shorter push rods in a couple of holes to get things adjusted right.
We don't have a tach in the KOH car, but comparing our engine to competitors who do run a tach, we have to be pushing about 7,500 RPM's on the high end. Who knows, maybe higher.
Also, the generate less friction, you have more control over valve train geometry and rocker ratio (you can get them in multiple ratios)..and they make more sexy.
If you wanted to get more info, give Russ Pottenger a call at Bishop-Buehl racing engines.
Bishop-Buehl Racing Engines
West Covina, California 91790
Work (626) 967-1000
Fax (626) 967-7836
Email RussBnBracing at yahoo.com