Variable geometry is more of a benefit on a small engine that is more prone to lag from limited exhaust flow. I would imagine the diesels might use it because they need to build boost right off idle. In a performance application on a V8 I don't think I'd bother, unless you are using a large turbo for extreme power you can size the turbo to have very good response without bothering with vg or other tricks....

 

Agreed. There seems to be a lot of controversy over this subject, but between all of the housings, housing sizes, and turbine and compressor wheel variations, you can build a really good turbo to "Match" your needs.