I think we'll have to wait and see. Its not really fair to judge the success of a 2.3/2.4 by comparing 'who is fastest'. The 4G63 in 2.0 form has has years and years of development compared to the 2.3/2.4 variations which are relatively new. Strictly speaking, not many people have 2.3/2.4, so by sheer numbers there are more 2.0s out there running around. So naturally there are many more fast 2.0s, simply from a numbers perspective.

I think as more and more people try the 2.3/2.4 combo we will see it becoming a more attractive option. With proper headwork,intake, cams,rod angles, and other motor tricks, there is nothing to really hold you back. If you can rev the same and hold the torque you will make more power, and its just that simple. People are trying 2.0 cams,intakes,heads on the 2.3/2.4 with so-so results. You need to realize, when you have a motor with vastly different requirements, you cant just use the same cam, head increase teh displacement and expect anything great. Thats why the results are so-so at best. But people are realizing this, and trying non-off-the-shelf cams (custom), and providing a proper intake (not a generic one designed for a 2.0 sheetmetal) and are starting to see the benefits of the displacement up top as well.

Sighting Shepherds car isnt a good idea. He has a VERY well working 2.0 combo, for him to try a 2.3/2.4 just for the hell of it is not prudent. He just can't waste that kind of time / money. Thats not to say its not a good option.

All in all, there just hasn't been enough effort put into the 2.3/2.4 yet. But more and more are popping up, and the results look good.