If you are already set on getting an FX-8350 as a drop-in replacement for your 965 @ 4.1, I would say good choice.
I have an old rig (not as old as yours, ~2 years old, although some parts like the vid card are a bit older) similar to yours, but it used to run a 1090T. Could only clock it reliably up to 3.9GHz.
Almost a month ago, was able to see an FX-8350 for very cheap, and since the board in that old rig can accept it, got the FX as a straight CPU-swap.
Even against an overclocked 1090T @ 3.9, a stock FX 8350 was no worse off in the benchmarks I ran for Windows and 2 Linux distros (CentOS 6.4, Fedora 17), a mix of single- and multi-threaded benches, slightly more ST though. I just quickly crunched some of the data I collected before and after the swap, and broken down per OS (all are 64-bit versions), the results are:
Code:
Advantage of stock FX-8350 vs 1090T@3.9
Win 7 Pro: +6.5%
CentOS 6.4: +0.55%
Fedora 17: +1.58%
So even before OC'ing the FX-8350, it's already no worse off than the highest my 1090T could go. In ST scenarios, your 965 has 200Mhz more power and so will be slightly better off, but in MT scenarios it won't be a match for the 1090T @ 3.9, so most of these results will be a "worst case" for you and you can expect much better improvement even at stock.
Also, at stock, AMD's CnQ is on for the FX, as well as the Linux scaling governer, cpufreq, being set to on. It is not a problem for most of the benches, but in certain ST benchmarks like Oracle, it lowered some scores by 10-40% (this is why CentOS 6.4 only shows <1% improvement). The 1090T@3.9 has both CnQ and cpufreq turned off. Turning off cpufreq (but leavning CnQ on) would increase linux scores by a few % overall.
Here comes the complicated part. The benches, depending on what they are and on what OS, show non-uniform improvement. Some benches show big increases, some ST benches are as you'd expect (slight disadvantage for Piledriver) while some actually show a hefty increase (20%, meaning clock for clock Piledriver cores would score better than Stars).
For example, in general the PHP benches favor Piledriver cores vs Stars, but the Python benches show the opposite picture. Results, but without the WHIRLPOOL results mixed in:
Code:
Advantage of stock FX-8350 vs 1090T@3.9
PHP Hash Bench: +9.35% //max turbo speed at stock of the FX is 4.2, only
//7.7% faster than 3.9, so seems PHP loves Piledriver
//cores more than Stars
Python Hash Bench: -11.72% //seems Python hates Piledriver cores
//or could just be the hashlib library which does.
I haven't run further tests yet on whether it is indeed only Python's hashlib that hates Piledriver cores, or the python interpreter itself.
For PHP benches that don't deal with crypto, results are even more advantageous for Piledriver:
Code:
Advantage of stock FX-8350 vs 1090T@3.9, PHP Bench, non-crypto
Windows 7: +15.89%
CentOS 6.4: +13.28%
Fedora 17: +17.33%
Clearly, the PHP interpreter loves Piledriver cores more than Stars. Results above contain 50% ST benches and 50% MT benches (simply the MT-equivalent of the ST ones); the ST benches, if separated from MT, range from 10%-24% (from all OSes) better. Again, since the clock advantage of the FX at stock is only 7.7% (and we're already assuming it will run at the max Turbo freq for the duration of the ST benches), everything above that shows favoritism to the PD core vs Stars.
Another example of "it's complicated" is the WHIRLPOOL hash algorithm, which is why I removed it from the overall hash bench results I presented earlier. The hash bench (both the PHP and Python versions whose results I presented above) is composed of the following hash algos: MD5, SHA1, SHA224, SHA256, SHA384, SHA512, RIPEMD160, and WHIRLPOOL. All these algos, except WHIRLPOOL, show consistent increase in performance, as expected from their platform (Win/CentOS/Fedora). That is, the individual results don't deviate from what you would expect based on the other relevant benchmarks in the particular OS tested.
However, WHIRLPOOL, like python, shows a consistent regression on all platforms, more pronounced on Linux:
Code:
Performance regression of stock FX-8350 vs 1090T@3.9, WHIRLPOOL hash algo only:
Win 7: -9.00%
CentOS 6.4: -24.38%
Fedora 17: -14.18%
There's a perfectly good explanation for this. Unlike the rest of the hash algos benched, WHIRLPOOL is based on a block-cipher. And in all other crypto benches I made, block ciphers (like blowfish) suffered a significant regression from Stars->Piledriver. Clearly, if your machine is meant to be a block-cipher churning super-machine, Piledriver cores are out of the question.
There are some other interesting data points, but you get the idea. Overall, as the first set of results would say, it is definitely no worse than a 1090T@3.9. The power savings are also significant. Compared to the 1090T@3.9, the FX 8350 idle power consumption is ~40W less. Load power consumption is even better, at ~70W less.
Clearly, with overall performance no worse than an OC'd 1090T, but with significant idle and load power consumption, it is (mostly) a no-brainer as a cheap CPU-swap.
The only possible drawback is if your specific use-case suffers from Piledriver cores vs Stars, such as (from my initial data gathered) block ciphers and python.
Anyway, good luck and tell us how it goes for you after you do upgrade.