They probably didnt use Apple's Xcode and probably have a shitload of PC code in there that doesnt take advantage of the G5's advanced technologies.

We've often heard about the "Megahertz Myth" -- the idea that Macs can perform as well as or better than PCs despite their lower clock speeds, and that's true for some operations. Games don't work that way, though: there's no substitute for CPU cycles when it comes to games like this.

Just like the PC version, timedemos should be run twice to get accurate results. The first run the game is caching textures and other data into RAM, so the timedemo will stutter more. Running it immediately a second time and recording that result will give more accurate results.

The performance differences you see between Doom 3 Mac and Windows, especially on high end cards, is due to a lot of factors (in general order from smallest impact to largest):

1. PowerPC architectural differences, including a much higher penalty for float to int conversion on the PPC. This is a penalty on all games ported to the Mac, and can't be easily fixed. It requires re-engineering much of the game's math code to keep data in native formats more often. This isn't 'bad' coding on the PC -- they don't have the performance penalty, and converting results to ints saves memory and can be faster in many algorithms on that platform. It would only be a few percentage points that could be gained on the Mac, so its one of those optimizations that just isn't feasible to do for the speed increase.

2. Compiler differences. gcc, the compiler used on the Mac, currently can't do some of the more complex optimizations that Visual Studio can on the PC. Especially when inlining small functions, the PC has an advantage. Add to this that the PowerPC has a higher overhead for functional calls, and not having as much inlining drops frame rates another few percentage points.

3. More robust and modern OpenGL implementation on OS X. The fact that OpenGL is engineered from the ground up on OS X to be accessible from many applications at once is wonderful for the rest of the world, but does have a performance hit for games. Sharing GL with the rest of the system invokes a small overhead that Windows doesn't have, since Windows can basically assume GL is just in use for one application.

4. OpenGL framework/drivers split on OS X. On Windows, ATI and nVidia are responsible for the OpenGL code all the way from the hardware to the game. On the Mac, Apple handles the top layers of OpenGL and then hands data off to the video card drivers. On Windows this allows the video card manufacturers to do some more direct optimizations that make sure data gets passed to the card as fast as possible. The Mac can't short circuit that process, since there is a fairly well defined boundary between GL and the video card drivers. This is complicated by the more modern GL implementation on OS X as well- Apple can't just put in a bunch of hacks to shove data around the wall and into the cards, just for the game.

5. And the last, but definitely most important factor: Amount of time Apple/ATI/nVidia have had to optimize specifically for Doom 3. On Windows, ATI/NVIDIA spent multiple programmer years tuning their OpenGL implementations for Doom 3, starting back over a year ago while the game was still in development. Apple/ATi/NVIDIA have done an immense amount of work on OS X's GL in the last 3-4 months, but there is no way they could get as much done as the dozens of Windows engineers working on the problem for over a year. 10.3.8 includes a huge number of GL optimizations that make a big difference in Doom 3, and the game wouldn't have been in any shape to ship without these. One of the biggest things ATi & nVidia do on the PC for Doom 3 is have application specific OpenGL optimizations just for the game. They can detect Doom3 is the application using GL, and even which shaders it is downloading -- then they can shift to a mode that is highly optimized just for those cases.

The good news on all of these fronts, especially the last one, is that Doom 3 is such a highly visible benchmarking application, Apple/ATI/NVIDIA/Aspyr are all going to be continuing to work on increasing performance over the coming months/years. Just like what happened with Quake 3, the Mac OS matured, video card drivers got more optimized, and the game was tweaked so that eventually Mac performance is now as good or better than comparable PC hardware (I'd be really interested to see benchmarks with Quake 3 with the original shipping Mac app & version of OS X versus the latest app & current OS on the same hardware). Games drive hardware and the OS, and Doom 3 will likely push Apple to upgrade consumer video cards and continue to spend engineering time in the future to speed up OpenGL.

My guess is that when Mr. Devine left, there wasn't anyone who could use a mouse.

I might as well hold out for PCI-Express and 3ghz dual core quads.