I just came across this thread and I have to say you shouldn't hide it that well. It really should be in some sort of "public library" with useful information, which applies to all mods.
I haven't tested it yet, but theoretical knowledge tells me this:
Expanding RAM address space:
I have known for ages that 32 bit can't access more than 4 GB RAM, which supposedly should be a prime motivator for moving to 64 bit systems. Don't listen to the talk about performance because some early 64 bit CPUs ran faster in 32 bit mode.
However I have always believed that 32 bit applications can use 4 GB when used on a 64 bit system. I have never heard of a 2 GB cap, though based on the description, it seems like a fair decision to add on 32 bit systems, meaning it's a relic, which we no longer need. I kind of suspect this to be a windows issue and that using 32 bit applications on mac or linux will not have this problem.
From a first glance, the only effect would be to avoid a crash when reaching 2 GB usage, which I guess is still the primary goal. However I find it plausible that it might improve performance in some cases. This would be due to memory fragmentation. If the game has twice the memory, it can spread out and can allocate twice as much memory before congestion issues appears. This is kind of like HD fragmentation. If you use 80% of a HD, it will be fragmented and slow down while using just 30% will counter most of this problem, even if you have the same amount of data on equally fast HDs.
RAM disk:
I have been using these on and off since the late 90s. They are great when used right, but used incorrectly you will not really gain anything.
Using memory has both higher bandwidth and lower latency. This means it will be insanely fast, but only if the disk access is the bottleneck. I once placed Neverwinter Nights 2: Storm of Zehir expansion in a RAM disk due to game breaking loading times. Turned out that disk access wasn't the issue, but rather what the CPU did to the loaded data, meaning the loading time depends on CPU speed rather than disk speed. NW2:SoZ was slammed in reviews for way to long loading screens, which often interrupts the gameplay, but it's actually pretty decent on modern hardware.
The improvement of using RAM disk increases the slower the HD is. SSD owners will see less of an effect and copying from a DVD to RAM disk will make a world of difference, mainly due to seek speed improvements.
Expected effects on Civ4: (any version)
Clearly expanding RAM allows bigger mods. It may increase performance in big games as well. RAM disk on the other hand will likely have less of an effect. Starting the game will likely improve, but the important part about performance is how long you have to wait for the AI. The AI doesn't use the disk at all, meaning I wouldn't expect any difference here whatsoever. It's also important to note that a not insignificant part of the loading time is the windows overhead from opening and closing a file, which will not be improved.
Autosaves have been mentioned as being faster and while it's most likely true, do you really want to save to a location, which is gone if your computer crashes? Savegames is likely the most important thing to store on a permanent disk. RAM disks should be for temporal files only.
