Upgrades

Hey there everyone, Today I have a question for Mac Pro owners. I'm considering moving from a PC to a Mac. I thought about a Macbook pro a few months back or even a Mac Mini but Both are so similar to my 1 year old Dell laptop that I want something with a little more power. I looked at the new iMacs released recently and one thing makes me reconsider it and that's an upgrade-able future. I've had a few desktops all PC's and one in which that has lasted is a Dell from 10+ years ago that just does not want to stop with it even supporting windows 8 come to find out. Anyway the new design of the new iMac is nice but I want to be able to upgrade something in the future. So that brings me to the Mac Pro even though it would be a hefty price compared to custom PC or another box from Dell or HP. I like windows 8 so far but I don't like how quick they change the entire operating system around. As for what I use a computer for.. It used to be I did all my gaming on it but have since moved to an Xbox 360 for most of it. I still play the Sim 3, Civ games and a couple other games like Battlefield 3 and Need for speed on my computer. I know as far as the processor is concerned the Mac pro has a decent one but the Graphics is a little out dated with AMD/ATI coming out with the 8 series on the PC side soon. But it says the 5770 has 1GB ram which should be fine but has anyone upgraded their mac pros past that. I've searched and searched for newer graphics cards but the 5870 was newest I've seen. So my question is would a Mac Pro be a decent moderate gaming machine. I already know it can do pretty much everything else I would need it to do. Also it won't be a bit until I decide to make the move so I may just wait and see if they do indeed release a new at the beginning of next year but I just wanted to hear from some mac pro users out there on how they like the mac pro.

Thank you for your response! I don't know much when it comes to mac hardware so the best option would be something I could just upgrade the machine without issues. I've seen all over the internet that the 5870 is the highest supported graphics card for the machine and that some have been able to get other cards to work but with some issue. I recently looked into some refurbished machines and of course looked at youtube and each one I've seen works great even ones from 2008 are still great machines. The only real gaming I do on the PC anymore is the simulation games that usually aren't good on consoles.

So with the Mac pro possibly out, what about the last gen of iMacs? I don't really want to go with it as its in my opinion a over-sized laptop in terms of you can only upgrade the hard drive and ram.