Is hyper-threading quad core or octa core no hyper-threading better for extreme multitasking?

I'd go with the i7…
http://cpuboss.com/cpus/Intel-Core-i7-4790K-vs-AMD-FX-9590
(Ignore the "review" section at the top, look at the benchmarks below.)
For starers, the i7 is still around 20% faster.
Having more cores doesn't make multi-tasking faster. Windows has been able to split up and run multiple processes on the same core since WIndows 95…

The next thing is reading reviews for the 9590, it's got more issues than I'd want to risk. A lot of chips dying…

Then, to keep the 9590 functional it needs a fancy cooler, which is money I'd rather spend on more performance. It uses around triple the power, which means you need specific motherboards to run the things, and a bigger power supply.

Basically by the time you figure in all the extra costs you might as well have gone with an i7.

I use a modified Dell Xeon E5-2699 Processor attached to 2 Nvidia Titans. I don't have this problem.

The AMD processors are also kinda Hyperthreaded, like the Intels. AMD's current architechture build around CPU's with "modules", and two cores per module. The cores inside a module share a few resources, like L2 cache, and FPU. AMD's implementation of threading is probably about 90% efficient at sharing resources with each other, without resource contention. Intel's may be more closer to only 70% efficient.

However, Intel usually enjoys a 20% single-threaded performance advantage over AMD. So the Intel will still end up faster overall.