Well done. Concise and to the point!
Although new to this site, I have to agree with your conclusion re: 595 vs 650.
I own the 595's and you describe them spot on, IMO. They do respond well to tube amplification, which is why I have a custom Ear+ HD Purist on order from Mapletree.
I probably would have gotten the PPX Slam from Singlepower, but for some technical issues and the fact that it is simply too big for my setup location.
I'm considering the 650's but they are similar to the 595 in many ways though, as you say, definitely more refined and not as open sounding. Probably will end up with K701's when they become more readily available, if only to have a different sound signature in my inventory.
Thanks again for the well written review and good luck in college.