No TIR? I was like that when I played AF when it came out, and I mainly did A-G stuff. I do hope you get a TIR, I can't recommend it enough. Flying without TIR is like flying an A-G mission without bringing a TGP.
As for your framerate problems, it could be two things: 1) Windows 8 or 2) weak hardware. As others have said, just because it's "new" doesn't mean it's more powerful than your 2008 iMac. Even if the parts installed are "new" in the sense that they have been released within the last 2 years, that doesn't mean they are powerful. Parts are released all the time and some are catered to the low-end, casual, mid-end, enthusiast, and money-burning-a-hole-in-my-pocket demographics. Best solution here is to post your system specs and let the community see if it is up to snuff.
As for the OS, any chance you can install Win7 or an earlier OS? If you have bootcamp, then I assume you have at least a copy of WinXP or Vista? Then try installing that in your new system and check your framerates. Remember to download the proper drivers for your hardware depending on your OS.
Good luck!
