Wiill the MSI r7 260 bottleneck my CPU?

nope

well, of the two, your cpu is far more likely to be the bottleneck then the gpu... that's an old and slow quad core. as for how you'd know you'd have a cpu core or cores spiking up to 95% utilization or so... with stuttering or such... same for the gpu bottle-necking you... only it would be the gpu hitting high utilization and the cpu doing little.

pretty straight forward. however in your case it will likely be the cpu that's the issue with either of those cards.

what specifically is your problem?

I think we're talking past eachother.

When i ask what your problem is, what i mean is, why are you looking for a gpu? what game are you playing? what game do you want to play? what's happening that suddenly put you in the mood to improve your hardware.

When you ask about bottlenecks understand EVERY single computer ever made, when running a game is bottle-necking somewhere. your computer can only run the game as fast as the slowest part. So if you go out and buy yourself 2 r9-295x2 gpus for some quad xfire action, and you get yourself some insanely overclocked intel extreme edition 6 core cpu, i guarentee you, even with that $4,000 put into your cpu and 2 gpus... you'll still bottleneck. likely the ram... possibly the cpu itself... maybe something else. somewhere, somehow, something will still be bottlenecking you.

The main issue is to make sure your bottleneck is at a point it no longer matters. Currently i have an FX8320... it's overclocked at 4.8ghz today, in the winter time here in phoenix it runs at 5.0ghz... i also have a r9-280x... neither part is top of the line, though both parts are firmly in the "2nd teir" of PC equipment. i have a single 1080p monitor with a 60hz refresh rate. That 60hz refresh rate is the key part to this whole story, because THAT is my system's bottleneck. My system will never be able to show me more then 60fps in any title because of my MONITOR. and believe me, while the cpu and gpu are 2nd teir, there isn't a title out there i can't max in 1080p up to 60fps with this current system.

While an i5 would probably give me better FPS, and a gtx 780ti would give be more FPS as well, i could NEVER see that "upgrade" on my system because of my monitor. In short, my bottleneck is my monitor. 9 times out of 10 when people come onto these forums talking about bottlenecks, or "my intel is better then your amd" they are really bottlenecked by a 60hz monitor, and all that money they threw at their intel i7 and 780ti is being bottlenecked by their monitor in such a way, if they say their system next to mine you'd NEVER be able to tell which one is better.

Now if i had a better monitor, one with 120hz refresh rate, THEN we could start to see that 780ti and i7 perform better then my system... my system probably would top out around 80fps in most things, depending on the title, either the gpu or cpu bottlenecking me in turn... that i7 and 780ti would both probably still max out every title (or almost every title) to 120fps... with neither ever bottlenecking the other, and the monitor still being the bottleneck... taking this example one step further, we could add 2 more 1080p monitors and play across all 3 of them, and force even the 780ti to become a bottleneck in our system.

so as you can see, even with top of the line stuff, at some point, something will bottleneck something else.

So my question to you, is what are you playing? what is your resolution and refresh rate on your monitor? what do you want to play?

if you have those answers we can start to address how to keep your bottlenecks invisible.

ok. ~ that monitor is approximately 85% the size of a 1080p monitor. roughly in line with a 1600x900 resolution screen. it's also capped at 60hz, so you'll never see more then 60fps in a title... so we don't need to worry too much about pushing the specs incredibly. a r7-260x should be fine for what you're looking to play. heck, even a r7-260 should be ok.

the issue you might run into is your cpu probably isn't. skyrim, tf2, fallout, even thief all love good cpus. and your's is not.

So here are some options for you~

1) you can get the r7-260/260x (there are some great deals on the 260x right now), and see what happens when you play those games. If you can't play them to your satisfaction i'll guarentee you 100% of the issue will be the cpu. from that point you'll need to look at new motherboards, new ram, and a new cpu. probably a $200 outlay at the min, and you'll likely have to do some overclocking at that price point to play those titles like you want.
~the new Pentium g3258 + a h87/h77 motherboard would be an attractive combo with 4gb or 8gb of ddr3 ram; that said you'll still need to overclock that chip a bit.

2) you can just scrap what you've got, start a new thread with a budget, and ask for the community to help you build a brand new machine. there are a lot of good part pickers around here, who can help you put together a machine that could do what you're looking for.

3) you get the r7-260/260x and learn to overclock that phenom quad core. that said i'm not sure even a heavy overclock on that chip will help it out in those titles... but it can't hurt to try. and this is the cheapest solution to the problem you're looking at.