Well, you still have other options available for security software. Avast, AVG, Norton, and McAfee all have been updated to work. I already addressed my unimpressed state over ZoneAlarm in an earlier post.
And people who rush out and buy things without checking to make sure they will work first deserve what they get IMO. Of course the owners of all three models probably don't realize just what a blessing in disguise it is that those things don't work. The one Lexmark printer I've ever own, mysteriously died on me after being left turned off for about 2 weeks. HP makes nice laser printers, but their inkjets are as big a pile of crap as anyone else's, plus their drivers are dreadful no matter what the model. Epson has never really been a major contender in the printer world for a reason.
There is actually a way around the signed drivers thing. You can either hit F8 at every boot, and there's an option to disable driver security checking, or there's a little program called ReadyBoot Plus which basically just automates hitting F8 every time you boot and selecting to disable driver signing checks. It adds about 10 seconds onto your boot time is the tradeoff.
On point two... I figured as much, but didn't care so much.
Onto point three... It's real simple. Most graphics work makes heavy use of 64-bit variables. On a 32-bit OS, you have to do 2x32-bit operations for every 64-bit variable. A 64-bit OS can do those operations directly, eliminating the overhead associated with a 32-bit OS. The catch is, the program and OS have to both be 64-bit.
Video encoders should see a significant boost, audio encoders, programs like AutoCAD and Photoshop... And games which have some kind of "64-bit enhancements" in them. I don't do a lot of PC gaming, so I couldn't provide you with a list. Someone said FarCry is among them. Never played it, only vaguely know it's yet another FPS, so can't verify the info personally.
I don't really trust benchmarking programs. There's entirely too many ways to screw up the data collection and taint the results. These can range from the unintentional, to the malicious. Microsoft will routinely pay to have studies done that shows Windows is better in some way than Linux or some other OS. If one research outfit doesn't produce the results they want, they'll keep shopping around until they find one that does, and we'll never hear about the 50 or so other studies that were either inconclusive or didn't produce the results Microsoft wanted. So there's often a financial motive. Then there's the possibility that someone prefers say AMD chips over Intel, so they might skew the tests in such a way as to be favorable to AMD chips. Like create a custom benchmarking program that makes heavy use of 3DNow! extensions which Intel chips don't support. It might be a subconscious effort as well, and the person isn't even really aware they're doing it. Then there's cases where ATI and nVidia have been caught putting special code into their drivers that detects benchmarking programs being run, and skews the results.
Instead, I like to look at the way things should be. Apps that use 64-bit variables will have less overhead on a 64-bit OS, which translates into increased performance. That's just a fact. Yes, poorly optimized drivers may affect this negatively, but that is transitory. Over time, the optimizations should improve.
I can say that a friend of mine bought an HP system about a year ago. It has an Athlon64 X2 CPU, I forget the clock speed offhand, but it has 3GB of RAM. From a cold boot, it takes his system several minutes to boot and reach a usable state. Mine takes around a minute to a minute and a half after I added all the software I use regularly. I don't think mine is significantly faster in terms of clock speed, and this was even before I configured Vista to use all 4 cores to speed up the boot process. I know for a fact that my friend is quite competent with computers too, so it's unlikely that it's due to some malware infestation he's oblivious to, or anything similar. So, there is really very little to explain the rather poor performance of his system relative to mine.
Of course this is getting away from the original topic. So I would again suggest that the original poster check on the compatibility of the programs they wish to use on their new computer. Separate them into two categories. One for programs that you absolutely cannot replace, and those that you can either do without, or could substitute for another if necessary. Same with hardware like printers.
If all the must-keep items are supported, then you can press on with Vista x64 without any real fears. You also have a little time to seek out and test replacement programs for those that may not be supported, but aren't critical.