I think when it shows its age, it mostly has to do with a few considerations:
1) You do need to overclock it to roughly 4ghz - 4.5ghz in order to have it really compete against newer cpu's.
2) Higher heat output and energy consumption, mostly to do with mentioned above - having to overclock were the power draw does increase cause of vcore increase.
3) Lack of certain connections - No USB 3, No M.2 slot, PCI-E 16x 2.0 rather than 3.0 (not really that important since so far to my knowledge, there is no difference in performance yet)
4) Dead Socket. No longer supported.
5) DDR3 instead of DDR4. This is a kind of bonus and not. DDR3 can be had for cheap. And since this is triple channel setup, performance of a 1333mhz Triple Channel does around same as 2400mhz double channel.
6) I think maximum supported speed of ram is 1333mhz with best of the processors (980x or W3680). I could be wrong on this.
Outside of that, if you can pick up something like a T3500 and a W3680, you can use throttlestop and get it to 4 - 4.2ghz no problem from what I am reading, and with 12gb of ram in Triple Channel all for probably around $150 USD. I mean, that is really good. If you can get a 2011 v2 or v3 though, you can also do equally well especially since they support quad channel.