Jeff Galloway's book can answer the question on how to correlate the run/walk ratio to a given pace using specific formulas, and from a given pace to the run/walk ratio.
The gains to walking inbetween running drop off quickly past the 1 minute mark according to some research Galloway gives or I read somewhere else.
From my experience the run/walk method gives your body a chance to recover, clean up some lactate acid, give your muscles a break, allows you to run longer, allows a faster method to change pace, and allows many short spurts of faster running.
These last two are my conclusions. Ive found that it is harder to run too hard when your taking short breaks because just changing paces by walking takes some effort in itself. Also Ive found that at a start of a run interval the easy pace is significantly faster than if I slowed down while running.
You might not run the same pace for any run/walk ratio for short distances unless that distance relatively long for you. For example if you cant run the 5k without stopping then 5k is long. Also dont assume that a 1 mile pace can be done over a 5k distance. If you look at the paces each world record is done at the pace will get slower over distance. Use the formula (your 1 mile pace)*(5k WR pace)/(1 mile WR pace) = your 5k pace.
I think if the run distance part of the run walk ratio is much smaller than the overall distance then you'll find that the run/walk pace is faster.
If you want an example then check out a 46 mile run Ive done using 5 min run 30 second walk (maybe 1 minute walk??) and the training I did to do it (not as much as you'd expect). Compare to a better trained 50k run but shorter without regular breaks. Sometimes checking out what other people are doing can help you achieve your goal too.
I advise you to buy Galloway's book because he tells you exactly what to do. Local running clubs are the next best bet and you can get your running questions answered while your running, or at breakfast afterwards with your new running friends (or old friends that are now running friends too).
Ok, last thing. Try 30 min to an hour of walking fast. Putting power into your hips, keeping your feet moving fast, and try to hit 15 min miles. Then aim for 12 min miles. I was surprised to hit a few 13 min miles while recovering from an injury, and I keep much of my speed from walking and biking during a 4-6 week recovery.