If the purpose of the cheques is to stimulate the economy, menaing you want people to spend that cash, you'd want to target it as broadly as possible. For those people on the upper end you can just claw it back in taxes later.
If the purpose is to help those most in need, then a one-time $1,400 cheque isn't going to make a big difference in the long run.
I guess it depends on the purpose of the cheques. You could give it to people making 100k i guess. I think i'd rather give it to middle class and poor people, they'll definitely spent it plus they need it more. 80k vs 100k doesn't sound like a big difference, those people won't go homeless either way.
I would think there's lots of people out there who need the money, maybe the focus should be on need. $1400 would be a big help to a lot of people living paycheck to paycheck or out of work.