Fair enough. The upper-mids spike makes the increased bass less noticeable in comparison to something like the DT880 or HD600 because it effects the volume level you listen at and can take your attention away from the bass and other frequencies. Additionally, the upper mids can be fatiguing at times when listening at reasonably high volume levels. Other than that these are fantastic. The soundtage and instrument separation is easily better than both the DT880 and HD600. These also seem to have, overall, slightly more detail than those two though I'm unsure how much of that is due to the sound signature and the improved separation as opposed to the drivers actually being more resolving.
They are extremely comfortable. They don't clamp very much at all which I could see bothering some people. The DT880 and HD600 feel more secure on my head and are more comfortable in that regard but the K712 are very comfortable. I like the memory foam pads a lot. I suspect they won't as easily become depressed over time as the velours on the DT880 and HD600 do.
Not sure what else to say right now. I like to really give a heaphone a lot of head time before i feel confident in all of its abilities/weaknesses/etc. I'm happy to answer any questions you have though.
I see you have a pair of pro 900s. Comparison of the bass?