Heres the developer's standpoint I was talking about:
On the average, when using Carbon, a program is already 90% done when the porting process begins. In contrast, when using Cocoa, you can only reuse the OS independent code. Porting to Cocoa is almost as large a project as porting from PC to Mac. You have to rewrite Messaging, Threading, GUI, 2D Drawing, Network, etc. Plus, you have to adjust to Objective-C. The cost difference between these two alternatives is large ... AND little of the advantage that Cocoa fans brag about has been seen (quicker time to market, faster code).
I like Cocoa fine, but I don't view Carbon as its red-headed stepson. Frankly I'm getting tired of people bitching about Carbon. Mac OS X would have a very rough road to acceptance without it.
To answer your question though, yes, the Carbon finder can be just as fast as any Cocoa based finder, assuming all the code (Carbon and Cocoa) is optimized with equal effort. I don't think the finder is done being optimized (its definitely better in 10.0.4 though!)