This is an attempt to provide a complete answer by summarizing bits from individual already existing answers, with some added content. The list tries to include all possibilities for a general case, even if some can be ruled out for this particular case.
CPU instruction set difference
As described by Joel Coehoorn, for a native x64 code a larger register set is available, as well as some additional instructions (e.g. all x64 CPUs are guaranteed to implement SSE and SSE2 instructions). This means native x64 OS and drivers can be more efficient.
Better RAM utilization
64b is able to use full 4 GB (and even more when available). Moreover, some OS internal limits (paged/non-paged pool, maximum cache size) are increased with 64b OS. As a result, both memory paging and file caching may be more efficient.
Different hard disc position
When you have two OSes installed on two partitions of the same disc, one of those two partitions is closes to the outer edge, which is generally faster.
Different OS state
When you have two OSes, each of them may be in a bit different state. One of them may be more fragmented than the other one, one of them may have a bit cleaner registry or less installed services or background applications than the other one.
Better drivers
Another possibility is x64 drivers might be of a better quality than x86 not because of some fundamental architecture differences, but simply because their vendor took more effort to optimize and fine tune them.
64b addressing
I add this only for completeness sake, as for vast majority of everyday applications this difference plays no role, and it definitely is not relevant to what Jasper describes in his question.
If you have an application which processes huge amounts of data (e.g. working in Photoshop with huge pictures), running 64b version can make a huge difference provided you have 4 GB or more of RAM installed.
What does "faster" really mean?
Here is the list from a comment on other answer, what exactly are the "faster things" Jasper can see:
- windows animating smoother
Hard to explain. Windows animation is done by the GPU in Windows 7 and the GPU is the same. The load on CPU is negligible. (I suppose you are using Aero desktop).
- certain photo editing programs drawing faster (both x86 and x64)
- HD videos running smoother (on MPC-HC x64), and an overall more stable experience.
Could be better tuned drivers or drivers taking advantage of x64, .
- files being copied a lot faster
Could be caused by a faster partition (not related to OS at all) or by better cache handling in x64 OS.
- The games didn't show any change.
Understandable. The games performance is determined by CPU and GPU. In case of CPU limitation the limiting code is the game itself, which is the same x86 code with little interfacing to x64 OS. The CPU performance is therefore the same. The GPU is the same. The driver and OS overhead in a well programmed game is low, therefore any driver or OS differences are not likely to show here.
Best Answer
In the days of Vista, A LOT of users were not happy about the experience yet still wanted DX10 Gaming and decent OS performance, so a movement started that introduced Windows Workstation 2008. You see the kernel was infact quicker in the server product, real world tests prove as much as 15-17% quicker.
Besides this, if you're a developer its often great to work directly on a server product, but at the same time you want to still keep your after hours activities (gaming, movie watching, etc) Your first answer is YES, all of these can be done on a server.
You will run into some practicality issues, but most of these can be overcome. For example - Certain AV products won't install on a server. But I've always found a workaround for this. Another thing is some Nokia phone software also required some extra hacking to get working, and at one stage even Windows Live Products needed to be "hacked" to be installable on a server product. Some old games that check for OS, also might not install on a server OS. Perhaps the biggest loss, Windows Media Center.
However the reverse is true, most server products can be "tweaked" to get to work on client systems. Take SharePoint for example - you can get that running on Windows 7, if you know what you're doing.
I am not sure if you're going to see any real performance increase in using Windows 2008 Server R2 vs Windows 7. Windows 7 sports a very well written kernel and explorer shell, and I have yet to find any convincing evidence that the server product is somehow quicker.
I guess its all about preference and experimentation, don't let anyone on here tell you otherwise. Do what you want, and enjoy the experience!
If you want some inspiration I would suggest looking at this web site: http://www.win2008workstation.com/
Enjoy and take care....