In order to even begin comparing these two Operating Systems in regards to speed (W7 vs. OS X), you'd need to start by running them on the exact same hardware. You stated that your W7 is running on different hardware, so from a scientific viewpoint your comparitive results can only be inconclusive at best.
If you are really interested in which OS runs faster, try installing W7 on your Mac using a dual boot partition (not in Parallel or any other VM ware, as that would make the two OS's split/share hardware assets like CPU and RAM). I haven't done this with Windows 7 yet, so I cannot accurately state any results.
Also, it is very fair to say that an OS will perform differently on different hardware. A system with last years CPU, GPU, etc., might be more compatible with a certain OS's programming code than a newer chip would be, in some cases.
'Speed' is also affected by how the program/app being used at the time is coded. Specifically, whether or not the programming code is fully utilizing your CPU/GPU features. This will, of course, depend on the app developer and the hardware you are running.
There are too vast a number of variables at hand to ever be able to state 100%, without a doubt, that one OS is faster than another. Mainly because speed will vary from one app to the next. That, and terms like "fast" and "speed" are far too broad to be measured.
Feature wise, it took me a little bit to become accustomed to OS X when coming from many years of using Windows. Once I did, and in the time since, I have found more useful features in OS X than I did in Windows. I would image this opinion would vary from person to person though, depending on what features you require most.
With regard to Linux, you are not quite correct. I can tell you haven't used Linux much, if at all. Ubuntu, the largest Linux distro, has an open source community comprised of millions of users. And that is just one distribution out of many (there are Linux distos to fit just about every lifestyle and personality). The Linux market share is just behind, if not dead even with, Mac OS X (Source: http://broadcast.oreilly.com/2010/09/debunking-the-1-myth.html).
Ubuntu Linux is known for its support community. And with regard to software, it natively supports more apps than you might think. It also has open source alternatives (some which I have found to be better than their proprietary rivals) to pretty much every app/program you can imagine... and even some you can't. Not to mention Wine support, which allows Linux users to run programs made for Windows. Though, I've yet to have to use Wine.
Linux is also great for programming and has amazing security (think government level), which is where its roots are. With Ubuntu however, the system has become very user friendly, elegant, and more often than not, it will work right out of the box.
Ubuntu was also the first to integrate Cloud support into its OS. Something Windows and Mac are playing catch up on at the moment. It really is very smart, intuitive, and globally renowned for its efficiency. The Linux kernel and open source drivers take advantage of features on the CPU/GPU of my old Laptop and Desktops that I didn't even know they posessed! They run and feel like new again because they are programmed to be less resource hungry.
So... Linux is no longer confined to programmers and government agencies, as many believe (the Android OS is actually Linux).
I am a total geek!!