I don't have issues with channel imbalance artifacts with my DT 150, and the DT 250 when I had it (sold it because I didn't like the coiled cable, it dragged down the headphone too much on my head, but that was before I knew that someone was making lighter custom cables for those headphones). I now have the Mogami 2893 mini star quad cable installed on my DT 150, and I feel it has made it slightly more clean/controlled as compared to the stock cable, but ofcourse with such claims your mileage may vary. The Mogami cable is way lighter than stock, and so I'm really happy with it.
I actually think the HD 540 Gold is more transparent to the source than both Beyers, but lacks bass impact to be neutral. DT 150 with stock pads, is too bass heavy and a bit boomy in the bass, but with DT-100 velours installed, it becomes a lot more neutral. I haven't heard the HD 250, so can't comment on that.
As for DT-250 vs DT-150, the DT-250 - 250 ohm (haven't heard the 80 ohm) is a bit more refined/controlled, smoother with better timbre. DT-150, with both pads, has a ''bigger'' sound, meaning instruments, vocals etc. all have a bigger presence, due to the bigger pads. Sound signature between the 2 (with DT-100 velours installed on my DT-150) would be pretty much the same.
Out of those headphones, I have heard the SRH 840. And the DT 150/250 are better in every category no doubt. Separation, imaging, resolution, definition etc, the Shure was a bit harsh/unrefined somewhere in the lower treble/upper mids, and sounds more plasticky in timbre as compared to DT 150/250 (or HD 540 Gold).