You have two DW's , a prep sink, and you're worrying about matching numbers at HD? When a good local plumbing supply would advise you on the disposals and air switch and may be a few dollars more? Okay. .....................

Buy more power than you think you need. For both. Watch what you put down there : )

You want a model with "40 oz. Stainless Steel Grind Chamber and Components". Other models with a smaller grind chamber do not use stainless for the chamber. It's composite. The blades are stainless. For longevity get a stainless chamber. The least expensive is often the Septic Assist version. Putting organic non grease/fat material down your septic disposal is very good for the health of your system. You don't need the assist.

Waste King 1 hp L-8000 - you can get a matching pair for less than one Evolution. Mine is spectacular.

Waste King L -8000

I don't know the model numbers you posted - it would help if you provided links. Regardless, for both sinks you want either a 3/4 hp or a 1 hp disposal. Not less hp than that. It doesn't matter if one is for a prep sink or not. They both need to be either 3/4 or 1 hp models.

Make note of where your plumbing under the sink exits into the wall. The disposal exit line needs to be higher than that, or it won't drain. This has come up on this forum before, and what people do in that case is get an Insinkerator Compact (still 3/4 hp, but a smaller chamber), or they have their plumber move the drain line down - not as difficult as it sounds.

As to air gaps, they are no longer needed with modern dishwashers which come with a "high loop hose" that works better than an air gap. Unless you live in California which has a Code that requires them. Even then, install the air gaps for the inspection, and when that is done, replace the air gaps with your soap dispenser or hot water faucet or air switch. Air gaps are no longer needed if the DW has a high loop hose (all the new ones do), but California for some reason is still 20 years behind the times.

Dan1888...it's Code in our area. When on septic, you are only allowed to put in a GD if that GD is specifically for septic systems. I guess similar to the places in California that require an air gap regardless of a DW's need, our area requires the septic GD.

I'm going to agree with Buehl on the prep sink needing a powerful disposal. We have both a prep and cleanup sink and knew going in both would require disposals. Went with 3/4 HP in both, which I find to be enough power - but I also put a lot of vegetable matter and other things in a small compost container I keep under one of the sinks.

If you don't have a septic tank, I like both Insinkerators and Waste Kings - I think both are good brands. You won't need air gaps unless it's required in your area. I understand many DW recommend you install them - our double drawer DW install manual recommended an air gap, but via questions to GW/Houzz'ers, we found it was (thankfully) unnecessary with a good install : )