The answer is... not nearly as a far as a SAS. (and I'm talking purely performance, cost not a factor).

case in point: Its not Isuzu specific, but a while back Walker Evans sat out to build from scratch the ultimate IFS buggy for competition rock crawling. I don't have to tell you he has far more resources and money to put at the thing than any of us do with our Zu's. The net result was a spaceage, long travel IFS design and high dollar Posche 911 CVs. How'd it fair in competition crawling? well, his buggy now sports solid axles if that says anything.

This case is more extreme than what any of us do, but you said "if built properly"... so here's a guy with virutally unlimited resources that did "build it properly" and in the end, choose to throw it all away for a pair of solid axles.

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my best advice: only pursue a monster IFS if you get your enjoyment from the fabrication process (and have money to spare). If you want the most bang for the buck, best offroad performance, and most versitale setup, you need to be looking at a SAS.

-Rob