OP has been updated with Case study breakdown.
Thanks! For simplicity's sake, let's assume you're making $80k. FICA/SS taxes will take $6k, federal income taxes will take another $8k or so, and state income taxes could be anywhere from 0 to another $6k, depending on where you live. Let's call it $3k for state income taxes. That puts your take-home pay at about $63k, with a monthly take-home of $5,250.
That gives you about $1500/mo surplus without changing spending. That's a nice situation to be in. That means your student loans are gone in 8 months. Once you sell one of the cars, you'll have another $400/mo, so you could be out of your SL's by 6 months.
Once you hit that point, you have $1900/mo, or $22,800/year. Here's what I'd do:
1) Max out the Roth IRAs (2x$5,500/year), to get a head start on your Roth ladder.
2) Put the rest in 401(k)s
3) Pay off mortgage and car loans at the normal rate.
You're both young, so your earnings will likely increase going forward, which would raise your effective tax rate. As it does you'll want to shift your contributions more toward the 401k/tIRA accounts. If you choose to have kids, that'll significantly decrease your taxable income, so you'll be able to contribute more to Roth at that point again.
You need a facepunch on your food budget. We feed our family of 8(!) on about $900/mo, and our kids eat stupefying quantities of produce, and meat of some sort is part of most meals.