Do you fly for Delta, as it would seem? Are you the one who decided to switch from the 737 to the MD-90 or 767 and chose the MD-90? I also can't imagine why MD didn't use an air scoop that generates less drag. I can't remember their name, but the scoops like those under the front of a L-1011 are the most efficient. The 777 also has the chunkier "square" scoops. Why? The L-1011 type generate less drag and have higher mass flows. I suppose that they're more expensive to make, though. I think the flat ones use see a lot of (especially on fast homebuilts like Long-EZs, Lancairs, and Glasairs) are called NCAA type air intakes. The lack the lip around the front edge that the L-1011's have.
I think you just have to know what an airline flies to know the aircraft. If it's American, you know you'll be on a MD-82. Ditto for Delta and their MD-88s. I believe TWA flies mostly MD-83s. The easiest thing is just to call them the following:
2. DC-9 Super 80 (my favorite, however MD-80 is also acceptable)
That's all the differentiation absolutely necessary. And I still think that MD-80/MD-90/717's climb better than 737s or A320s.