super lagggy

Hey how's it going everyone.
I have a quick question. I want to up grade my video card, but don't want to change the processor or anything else. Like i want to upgrade the card that sit fits my system specs, not sure if you get me.
My system spec.
Windows 7 professional 64bit
AMD Athlon 64x2 Dual core Processor 5400+
5G ram / ATi Radeon HD 4650 1G
480W power supply

i posted this twice on a different topic since no one was replying

If you can get your hands on a 5850 that would be a good buy, they basically sold them out and never restocked when they released the 6950 so it might be a bit hard to find. My specs are very similar though and it's what I'm using I have no complaints. I think going anything higher is just going to lead to some really annoying bottlenecks. Plus I've played everything in 1080p so I'm happy with it.
Then again it may also be among the best choices given your power supply.

I don't really know which nvidia would be it's equivalent though.
If price is not a problem by all means go with a 4xx series nvidia.
I honestly don't see the point in going to the absolute newest model card from either company as you'll still be suffering from some drive lag anyhow (newer games just don't precache...)

bottlenecking won't actually mess up the system, it will create noticeable frame rate drops in larger areas, or areas with a lot of shading or tessellation.
Since your system is about the same age as mine the biggest problem with newer games is really the slower reads we get from our harddrives, because less and less are they precaching entire levels like they used to, and try to load textures and stuff on the fly more now. This leads to some hiccups with the older hard drives. These manifest as graphical hiccups or even a second or two of stuck frame in severe cases.
It's a hard drive thing more than a graphics thing though.

like I said I am happy with my 5850 for what it is.
I'm as fond of it as I was years ago when I got the 8800gtx's I replaced it with.
I can also tell you the 1 5850 I got made more than a replacement for 2 8800gtx's that I had overclocked in sli.

So no doubt it's an upgrade to what you currently have.
The 5 series are honestly a little worse with dx11 than the 6 as well keep in mind that difference is more with the 69xx cards than the 68xx as said above they changed the system, enough to mean a bottleneck I can't answer that from personal experience.

TBH, Im not sure bottnecking will be that much of a issue unless maybe on something like a 6970 or GTX 580.
Or, if running a Crossfire/SLI setup.

But for most Mid Range, single card steups, you should be fine.

Sure, there may be a few games thats CPU intensive, or really recommends a Quad Core, where you may see some .. but overall it shouldnt by that big of a issue.

Or at least I wouldn't think so.

Perhaps in the 6000 series the 6850 or 6870 would be a good choice?
The 6850 will require a 500W PSu though, and as you go up ... 6870, 6950 etc its going to require more.