Hi, Ted
First, the issue of 64-bit verses 32-bit might give you huge problems when it comes time to consider 32-bit and 64-bit programs. Some programs absolutely run only in a 32-bit or a 64-bit system. :!: The good part is that CoD, RoF, and IL-2 1946 will run best in 64-bit. The bad part is that some software applications only run in 32-bit so there might be a conflict if you want to run a 32-bit program in the same system as your 64-bit Operating System. The three simulators themselves should run well in 64-bit, though you might need to do a few things for this to happen.
I'm sure you know that a dedicated graphics card is a must to handle all those programs with good image and performance.
PC and Macs will run any of those flight simulators quite well if you get compatible specifications and you are willing to do some work with configuring the programs and possibly handling drivers.
A 1333 Mhz DDR-3 or better is a must for running all of those programs with good performance. Try to get DDR-5 if you can.
If price is very important, then you probably will lean toward a PC with ATI/AMD graphics card. If I were not concerned with money, then I would get a high end Mac with NVIDIA 650 or higher running 64 - bit Bootcamp for XP, but extra tasks will be required to get all those programs running well.
Caution: The 32-bit programs against 64-bit programs is going to bite you eventually in your system. One could make a good case that a Mac with bootcamp 64-bit would be your best option to run all these programs but you will pay the price in both money and learning new skills.
The conflict between the 64-bit and the 32-bit is going to give you hoops to jump no matter what you decide if you want to run IL-2 1946 and any of the 64 bit programs in the same computer as well as choosing among 32-bit and 64-bit Windows XP through Window 7 programs besides these simulators. In my opinion, the conflict can not be resolved easily by most people out there. Your going to need to be savvy to handle everything. Are you ready to do the research which is required to learn this?
PCs
The Asus N56VZ-S3087V 15,6" LED Blu-Ray, Nvidia GeForce GTX660M Graphic card, Intel i7, 2,3GHz, Nvidia GeForce GTX660M has the fewer driver problems but performance is less.
Asus N56VZ-S3087V 15,6" LED Blu-Ray, Intel Core i7-3610QM, 3,3 GHz, 8 Go, stockage : 1 To, NVIDIA Geforce GT650M is what I would prefer. Though the GT650 has more driver problems, I would chose driver problems which are usually easier for me to fix than hardware inferiority.
Take a look at the MSI for comparison:
http://www.msimobile.com/level2_productlist.aspx?id=6
* For PCs, are you going to need a special partition for IL-2 1946? Special partition is not needed with Compatibility Mode For Windows XP Service Pack 2. Will you need to run IL-2 1946 in Compatibility Mode For Windows XP Service Pack 2? This Compatibility Mode should be used for Windows 7 and 64-bit systems. After this, if these do not make IL-2 function, then there are utilities to make this work. How are you going to run 64-bit programs and 32-bit programs in the same Operating System? You need to know what is the operating system which is required for each program and weather it is 32-bit or 64-bit. CoD, RoF, and IL-2 1946 can be run in 64-bit, but other programs might not run at all in 64-bit even with Compatibility Mode.
Macs
Bootcamp allows you to bridge compatiblity issues if you get the right one for your programs.
Yes I say to everything and add that for COD in a Mac, look for 64-bit bootcamp and at least a 5000 series HD Radeon or at least a 500 series Nvidia graphics card. CoD should be run through Bootcamp Windows 7 64-bit, though graphics card drivers might need to be changed if performance is poor.
To run the high effects settings in UP, look for both high system ram and also good video ram in your computer. UP also has performance enhancements built into this, so I would not worry about performance issues here in a Mac. For a Mac, you will need to experiment to see if IL-2 1946 runs better in Bootcamp XP or Bootcamp Windows 7, but I would start with Bootcamp Windows 7 64-bit.
Rise of Flight is unpredictable with drivers. For a Mac, RoF runs best in bootcamp for Windows 7 64-bit, but graphics card drivers could be an issue.
This is your most important consideration: In using a 64-bit computer system, some of the 32-bit programs out there not work because of unfixable driver incompatibility if you want to keep the best drivers for the simulators which you listed. The Windows 64-bit system allows better performance and more effects quality in CoD, RoF, and IL-2 1946 but some 32-bit programs can not be made to work in this 64-bit system.
For all the above reasons, you must be ready for the possibility that you may not be able to get all programs running well in your computer.
Fireskull