The K240 Studio actually has some good bass believe it or not. It's not even remotely bass light. Strangely there is more out of the box than after burn in somehow. I wouldn't get the MK2 unless you need the extra cables and pads. They both use the same driver. If you need the extras and it's only $20-$30 more it may be worth it.
The HD-595 will be slightly more comfortable for gaming. If you are eventually set on getting the 595 I'd suggest spending an extra $30 or so on the 598. Two websites have them for $175. JR.com does sometimes if you call them.
I prefer the K240 over my modded HD-555 (similar to the 595 I've heard) by far. Both are similar but the K240 has more bass and better mids. The sound to me is also much more clear. The K240 Studio is also under $100 and can often be had for just $70! You can even use the Beyer Dynamic Velour and pleather pads on them (don't try it if you already have a Beyer headphone. It stretches the pads and ruins them for use on the DT-880!).
The soundstage of the 595 might be slightly better, but I never compared them. The K240 is semi-open and the soundstage is OK, but nothing special.
HD-598 is what I'd suggest if you can spend a little extra.
BTW the K240 Studio seems to have about the same amount of bass as the SRH-840 (another old favorite of mine). Check out this graph! Very similar.