There is heaps of good advice in this thread and folks are genuinely interested in helping the OP. This is what you would expect from a knowledgeable and dedicated community. But it seems to me that not everyone has given enough priority to OP's needs and their intended computer use:
It is clear that their main activity is office productivity. These scenarios rest on high IPC, not core count. Also the general "feel", or responsiveness, of the system will be largely influenced by higher IPC and clock speed - rather than taking advantage of multiple threads. While I wouldn't call the i7-3820 "sluggish" or "obsolete" for office use, it is plain that the OP would really benefit from having faster cores, not more of them. Even a contemporary 4c/8t CPU will fit the OP's needs perfectly.
As one who has firsthand knowledge and years of experience with the X79 platform I've learned that more cores make a huge difference and do so at lower CPU temps. Also, replacing an 8 core 5960X in X99 with a 16 core Xeon E5 2683 V4 running at half the clock speed yielded things like A/V transcoding being much quicker at far lower operating temperatures. I'm currently in the process of replacing an ASRock Z87 Extreme6/4790K w/32GB of RAM with an Asus X79 Sabertooth/Xeon E5 1680 V2 w/64GB of RAM. I have an identical Sabertooth/1680 V2 in another rig and it blows away the Z87 in every aspect. 8 cores vs 4 at the same speed (4.5GHz) with the same cooling setup runs vastly cooler under load. The Xeons are better silicon than the i7's.
I've noticed it being stated that 8GB (2 x 4) of RAM is "enough". X79 is a quad channel memory platform and only using half of it is a huge waste of potential resources. 4 x 8GB is the minimum (32GB) for any type of production work. I've tried 4 x 4, 4 x 8 and finally found the best to be 8 x 8 (64GB). Faster clock speeds don't allow you to have more windows open, more system resources do. A 4c/8t CPU bottlenecks what the X79 is really capable of doing no matter what clock speed it's running at. I had a 3930K running at 5.02GHz in one of my X79's and a 1680 V2 at 4.5GHz absolutely killed it in benchmarks and actual use plus runs cooler. I had a 4960X in that same rig before the Xeon and I sold it as soon as I put the Xeon in.
I just looked on Ebay and the 1680 V2's start at $120 now, they were at $90 a few weeks ago. the 12 core 2697 V2's start at $135 at the moment, they were $120 a few weeks ago and there was one last night for $125. Lex's preferred 8 core locked E5-2667 V2 is at $119 to start with. There no way a 4c/8t CPU will come close to any of those no matter how fast it's clocked. On the extreme side of things I have a 22c/44t E5 2699 V4 w/128GB of RAM in another X99 and it beats my i9 9900K/Z390 Asus Maximus XI Hero Wi-Fi at 5.2GHz with 64GB of DDR4 3600 in transcoding and barely gets warm doing it. Less than half the clock speed but almost 3X the cores.
