I have GMR's 577's which are nearly identical to the 24D's.
The bottom end is softer than the 255's, not a lot but it is noticeable. Very slow speed riding is a little choppier than the 255's. They do run out a little farther in the rpm than the 255's.
Yesterday I ran my buddy flat out from 1st thru 6th Gear. He has a 2010 and I have a 2011. Both CVO Streetglides, V&H tru duals, we way about the same and our slip-ons are pretty similar. He has cobras and I have reinharts.
Both bikes run pretty damn close. Who hit the throttle first, who shifted better would really be the difference. As the 577's ran a little longer I would pull on him but would not outrun him. If you are expecting to blow doors with cams only don't set your expectations too high.
By the way, two CVO's wide open thru 6 gears side by side sounds really cool! Neither of us knew how fast we were going because we never looked down to see.

Overall I like the positioning of the power through the rpm range better than the 255's. But I do miss the low rpm grunt of the 255's.
With that said these cams will perform significantly better with compression set at around 10.2:1. It all comes down to the budget. Cams only = a little boost for low cost. Cams + Head+ Throttle. Body = Much more power at a high cost.