Depends on the discipline I suppose but if were talking trap for example DTL, to get the best out of a high rib is to use a high gun hold, you then look down through the rib to the exit point or in other words to the trap house lip, you therefore see the target early (which you couldn't do as well with a flat rib as the barrel would obscure most of it) but your barrel is already on the correct horizontal plane, you then just wait for the target to pop up above the rib and minimal sideways movement and jobs done. imo if you shoot a high rib the same as a flat rib (and hold on or close to the mark) then all you will gain is a head up position, it is my opinion that a high hold is essential in order to get the most out of it. There not for everyone and the above technique does take some getting used to but of course some people seem happy just to have the head up advantage.
Only my opinion of course but for the record I have had high rib guns in the past and was shown the above technique by one of the best DTL coaches in the UK.