Multi-Boot:
Standard Boot (traditional OS install):
Good: With this you can use the OS that the game was created for - i.e. 8/7/Visata, or XP, or 2000/98, or 95, etc.. That's the good part.
Bad: There are two bad things about this though as you move to earlier generations of OS's: (potentially) the hardware may result in a game running to fast; (likely) there won't be critical drivers available for OS - drivers like video drivers for your fancy video card, drivers for your cool peripheral (like a game pad or control pad) - think of USB's alone, etc..
Critical point: The real demarcation point in OS's was 32 bit XP for most games. Virtually any game designed to run in 32 bit XP will run in the Vista OS grouping (irrespective of a 32 bit or 64 bit OS) - see "run in Compatibility Mode" by right clicking the game's executable file. Compatibility mode can also work with even older OS's - but not always with the same dependability/consistency. Unfortunately some of the best games ever made (so far) were in the 2000/98 grouping. Despite this though, many of those excellent games have been altered/patched/ported to the higher Windows OS's (previously mentioned). GOG.com has a very nice listing of those older games. Again though, you can always try Compatibility Mode.
IMO because of a source like GOG.com - utilizing an older OS is largely irrelevant on new hardware. The new hardware is plenty fast enough for "heavier" newer OS's. It certainly isn't an improvement with respect to video performance. That pretty much leaves the disk system: and the disk system can be improved with SSD's or even software RAM disks, system process utilities like Process Lasso, and even system designs like one OS for each game. (..that's the likely area where XP 32 bit results in a performance edge over newer OS's.)
Virtual Machine Boot:
VM's are generally only acceptable in a system "Boot" configuration. Again, everything *but* the disk system is normal (i.e. "Bare Metal"). Particularly your Video Card runs normally - even if using multiple Video Cards in SLI or Crossfire.
The EXCEPTION is legacy hardware for legacy games - where the hardware virtualization of the entire system in software like Virtual PC, VM Ware, or Virtual Box, is acceptable - and perhaps even useful to "slow" the game down. This also gives you access to those USB devices you are using. (..IMO this is your last resort for an old game - i.e. can't find patches for it, can't find it on GOG or similar sources, can't run in Compatibility Mode, etc..)
To me Boot VM's are really only attractive because of:
1. Disk Space conservation with respect to a 1 OS to 1 Game design format. (..utilizing "differencing".)
2. Resiliency. Or basically it's easy to back-up - it's just an image file so you can keep multiple copies of it in different mediums/types of drives. Very easy to mount it to the newer Window's Boot Manager from any drive source.
3. Hardware independence (..which is really a subset of Resiliency). A VHD (or VHDX) can be used on any computer that has the appropriate boot manager for that disk "file" type (i.e. newer Windows Boot Managers). This is under a "generalized" system (..as opposed to a "specific" system to that hardware's codes).
You can also achieve a small measure of "hardware independence" with a traditional multi-boot system via a few back-up software applications with the ability to "restore to dissimilar hardware" configurations (i.e. Shadow Protect, Macrum Reflect Pro, EasUS Todo Backup Workstation, etc.). There it's more "A" *OR* "B" for your hardware - specifically as *restoring* the system, not "A" and "B" - or in other words not concurrently allowing you to use either system at any time. Even with these backup programs - it's a more involved process on the "restoration" end.
(Personal Note: I'm working on *2* systems to achieve some measure of fault tolerance, but the second one likely won't be finished until late 2013 or even mid 2014. The important part of the design with respect to hardware independence is that the VHD's will be on SSD's that are on "hot swap" hardware. I can simply pull out a tray with an SSD containing the VHD's and literally plug it into the newer design once it's complete. ..or at least that's my current plan. Should one fail, I have the other system as nearly instant "back-up" - all while maintaining a high bus rate via SATA 3 - as opposed to a currently slow NAS solution. Who knows though, a cheap high speed NAS box with Thunderbolt might be available at some point.)
Extra RAM:
You can in fact use that additional RAM with XP 32 bit - as a software RAM drive.
(..the OS couldn't use it though).At 4 gig for RAM and the OS I don't know what the limit is with respect to real performance and any paging file. You could however use some of the RAM (..say 2 gig) for your paging file (or Window's Virtual Memory).
Do a search on software RAM drives if you are interested.
RAID cards:
Yup, generally avoid - even the SSD caching ones. DEFINITELY avoid it for a boot drive (or your first OS boot). Also, there doesn't seem to be any performance benefit over that of a Cacheing SSD.
