School me on video cards for Linux

Ok ...here's the deal, I'm trying to gather what I need to make the switch to Linux in the next few weeks I have a pair of GTX 560Ti's in my computer that have been very good cards, but I'm wondering if I should consider changing to newer ATI/AMD cards? something like the R7 250 or the R7 265? how about the bus, 128 or 256? I like to stay a generation or two off the bleeding edge when it comes to GPUs just because I'm not a big gamer (although I do play one AAA title) and the cost to me just doesn't seem to be worth it.

I'll probably be running Ubuntu/gnome, and running Win7 in virtualbox, I'd like to try the hardware pass through, other than that I don't have anything out of the norm I'll be running.

My question should I just use the 560Ti's (I actually have two pairs of them 4 total)
Switch to AMD (will life be easier with the AMD cards?)
If I switch should I get the 256bit or is 128bit fine?
I don't think I'd buy 1gig cards probably 2gig cards but I do plan to buy a pair of whatever I switch to if I switch.

I guess the only other question you guys might have is the cpu will be a 8370 w/16gigs on a asus 990fx board ( I don't remember which model, I'm going to steal it out of my wife's computer and give my old 2500k which she likes better....lol, she has a pair of R7 265's in her computer that she said I couldn't touch, she hates Nvidia for some reason. )

What's your thoughts?

What do you plan on using your computer for?
I have 16 GB of ram and I'm running out of ram hosting a mc server and running one vm not to mention the absurd amount of ram that chrome uses.

Edit: Then it sounds fine to me I apologize that I cannot help with the gpu as I have only a single gtx 660 which works flawlessly with the mamarley ppa

Daily driver, I have a ubuntu server running to handle all the heavy lifting, so just your basic desktop, doing basic stuff.