Popular Hot Rodding did a three cam comparison on a near stock LS1. They tested COMP cam's XR265HR, XR275HR and the XR281HR. Output was as follows.....

Stock LS1
407 HP @ 5500 rpm
375+ lbs-ft @ 4800 rpm

XR265HR
439 HP @ 6000 rpm
426 lbs-ft @ 4800 rpm

XR275HR
450 HP @ 6500 rpm
422 lbs-ft @ 5000 rpm

XR281HR
455 HP @ 6200 rpm
421 lb-ft @ 5000 rpm

All this was on a motor with no accessories, running an electric water pump, Comp cams 918 springs, AccuFab billet throttle body, Wilson billet fuel rails, Hooker long tube headers, Pro-M mass air meter and meziere electric water pump. They thought the engine needed better breathing for the 281 cam. All testing was done without changing the PCM basic programming.