I think the question most people have is WHY would you do this instead of saving upwards of $60 and getting the 8350 which is known to do 4.6ghz on a regular basis without much, if any, voltage increase, and 4.7ghz with much less than 1.46v.
Thank you for your question and I will be more than happy to answer it!
1. Guaranteed clock speed. There is no way to know what you will be able to push a FX 8350 to. "Known to do" is a gamble. When I buy a 9590, I know that I will be able to run it at 4.7-5.0Ghz. I have read people buying multiple processors just to find one with a good overclock speed. No thank you.
2. I would like to mention, that I plan on reducing my voltage. My system is solid at v1.45-1.46, so I think I have some room to play. Given how cool it is, I may be able to get the voltage down to v1.39 or push the clock up to 4.8Ghz.
3. I will spend the money on a closed loop cooler, but I am in no rush to. I am currently playing The Division and I stream it a little. I get 30-40% usage on the CPU. When I do have a closed loop cooler, I will run it at 5Ghz and maybe push it to 5.2Ghz.
4. Your math is off. The cheapest I have seen the FX 8350 is at Micro Center. That is where I purchased my FX 9590 for $179.99, which is just $30 more than the 8350. $30 more for a processor that is guaranteed to run 1Ghz faster? Why not!?
5. Lastly? Because I knew it could be done. My last build was damaged in a storm. I was able to salvage most of it and got it running. It wasn't 100% and had some quirks. So I made sure to pick out parts that could run a FX 9590 and a case there is nearly a wind tunnel.
Quite a few knowledgeable PC enthusiasts run FX-9000 series or overclocked FX-8350 CPUs running at 4.7 GHz. or higher frequency using high end tower style HSFs. In either case running an FX 8-core processor at frequencies > 4 GHz. requires a high performing HSF. I personally have run 25 hour P95 durability tests on 4.7 GHz overclocked FX-8350 CPUs without any overheating using the Xigmatek Aegir SD128264 HSF. I can recommend the top 6-7 AMD rated HSFs at FrostyTech for FX-9000 series use unless you have some very uncomfortable ambient room temp such as >85F. Scroll down to the AMD test results as CPU coolers can perform slightly different on different sized CPU lids.
As you note it's important to have good airflow thru the case to remove the heat in addition to a properly sized and capable HSF. AMD recommends a specific class of water cooling on FX-9000 series CPUs because so many people do not understand that a 220w CPU requires a high end CPU cooler. (Note: H100 class and lower performing liquid coolers are not usually capable of properly cooling FX-9000 series CPUs properly.) Thus when an AMD FX-9000 series CPU customer uses an undersized HSF or liquid cooler they incorrectly conclude that the CPU is defective and they return it under warranty when there is nothing wrong except an undersized CPU cooler was employed allowing the CPU temps to exceed the 61C AMD max user specified temp for FX-8000 series CPUs.
The benefit to buying an FX-9000 series CPU is that it's plug and play assuming you use a proper mobo designed for the 220w CPU (another common problem) and it comes with a warranty vs. personally trying to figure out how to overclock an FX-8350 or similar to 4.7 GHz. with P95 stability. While AMD leaves the CPU unlocked for those who desire to overclock, technically overclocking voids your warranty.
It is refreshing to have some actual input that provided me with something to read up on. Other than a bunch of Novices trying bully me into their way of thinking. Thanks for the great reply. I was thinking about getting a Kraken x61, btw.