The -900 and -1000 can only be compared to a DC-9 in the number of seats each has. There's little else that can be compared, whether it's comfort, headroom, shoulder room, and cargo room, not to mention others. I find the -700 seats incredibly uncomfortable by the time I arrive in ABE from CLT. I can't even fathom how much my a$$ would hurt flying from CLT to DEN.