Okay, so I'm thinking of doing a post-christmas upgrade. Specifically, my CPU and graphics card.

Right now i'm going from an AMD FX 4170 to a FX-8350. And I'm thinking about the card.

At the moment I have two Nvidia Geforce GTX 560's and I'm thinking about going to a single GeForce GTX 780 3GB. Is that a good idea or no? (Not factoring in cost here.)

I should mention that I would like to run things like Better Cities/Open Better cities, and that currently I have two monitors (but I only use one for gaming. I use the other for playing movies in the background and stuff.)

Are you asking this for Oblivion only? Any good card would do for this game. Now, if you want something that will be able to run future video games, what does your retailer say about that?

SLI or Crossfire is not that good a system to begin with. Has to do with the lag and timing of parsing the video processing across two or more boards. IMO, it is just a way for video card manufacturers to get people to buy more cards. You are always better off with one good single video card than with multiples. Sure, you may gain some Framerates over a single card system, but you are usually already near or over 60FPS with a good single card, so any gains will not be noticed in the game. This also applies to the Dual GPU single cards that are offered. Though the lag and timings are better handled, the fact that most games are not optimized for dual GPU's is still a factor.

Multiple monitors and ultra high resolutions may benefit from multiple cards, if the game can even make use of the technology, which most don't.

Both, actually. I mainly stick to oblivion, but I do venture into fallouts 3, NV, and Skyrim a lot. And Fallout 4 when it comes out. And a few other games on a rare occurrence.

Plus I"m actually more concerned with maintaining a constant 30-60 FPS even while in betteropencities and not having it shift down to 20-10 fps outside and stuff, than I am in seeing how high my framerate can get (I don't find anything beyond 60FPS necessary)

As for resolutions, It never goes beyond 1600x900 (that's how big my "primary" monitor is, and I always play in Fake Fullscreen mode.) And I never actually put the game on the secondary monitor. It's just there to view other things (IE walkthroughs console codes movies etc.)

Okay so Single Card it is, then?

Yep, it's really the way to go.

I agree that one better card is the way to go. I recently had to go with a second card due to the fact that neither AMD's or Nvidia's cards this generation had a significant performance improvement. A lot more games are supporting Crossfire/SLI now than they were a few years ago, but again, you have to wait for AMD/Nvidia to release a driver to support the specific game.

Nvidia has a pretty good solution to combat the frame timing issue or "microstutter". AMD's isn't as good, since its only software based instead of hardware.

Either way, I'd go with a single more powerful card now, and in the future you could worry about adding a second card if you want a boost.

Edit- Also games like Oblivion, Fallout 3, NV, and Skyrim are all open world games, and load a lot of things at once. So you are always going to have a slight drop in FPS when that happens, even on an SSD I've noticed.

Single card is always better solution than CF/SLI. It may not give you best overall performance but at least you won't be suffering from a pile of possible issues like uneven performance scaling (in some games performance may be even worse than with single card) and microstutter.