Actually, it looks worse than "really close". I might not even be able to use a 7" depth + GD. Not sure, though.

There is no rough guide, except maybe to put the drain arm as low as possible.

Stick a 12 inch deep sink and a large GD on it and you need a pretty low arm.

Use a 6 inch sink and a ting GD and you might get away with only a foot below the counter.

You can easily cope with an arm lower than optimal.

An arm higher than needed often requires opening the wall (sometimes after removing the cabinet or it back) to move the arm lower.

The drain line into the wall cannot be higher than the waste line from the disposal. Otherwise you would have standing water in your disposal. More vertical separation is better.
On mine, this means a minimum of 8 vertical inches from the bottom of the sink to the bottom of the drain line.

Thanks for the comments. Accounting for the trap connection, I had eye-balled it at needing 10" from sink bottom to drain center - but if you managed an 8" difference, that's great and I could probably do it. Thanks again.

Here's the update:

Counter height ending up at 36 1/4"
(Drain center was 22" up from the floor)
Insinkerator (Badger 5)
Moen 6 1/4" deep drop-in sink (I found one that was boxy and not too rounded near the sides, so it didn't "look" shallow.)

I ended up with exactly 1" to spare on the vertical part of the disposer drain elbow, so a 7" deep sink might have worked, but it would have been really close.

Cheers.