Are there any scales that work well over this progression? My Mistake!! I was thinking of the song Breezin' by George Benson!!
I think maybe a quick overview of Diatonic Harmony would be helpful and make the numbers make sense.
As you may know, a major scale has the same intervals no matter what note you start on. From the root note, the interval are: whole step, whole step, half step, whole step, whole step, whole step, and half step. If you start on C, for example, and follow those intervals, you get C - D - E - F - G - A - B - C.
At the risk of sounding repetitive, I'll repeat the key point: the intervals are the same for every major scale. So no matter what key you're in, the third note in the major scale in always two whole steps away from the root note, the fifth note is always one-and-a-half steps from the third note, etc. etc.
So now imagine building a chord by stacking thirds on the root note, i.e. build a chord using the 1st, the 3rd, the 5th, and the 7th notes in the major scale. You get a Major 7th chord. If you're in the key of C, you'll get a C Maj7. If you're in the key of Eb, you'll get a Eb Maj7, etc. Because the intervals in the major scale are the same no matter what key you're in, the chord that you get from stacking thirds on the first note of the major scale is always a Major 7th chord. This is called the I chord.
Okay. So now imagine building a chord by stacking thirds on the second note of the major scale (in C Major, that would be D - F - A - C). Again, because the intervals in the major scale are always the same, you know that you'll always get the same type of chord---in this case a Minor 7th chord. Because it's the chord you got by stacking thirds on the second note of the scale, the chord is called the ii chord (we use roman numerals to number the chords, and we use upper case for major chords and lower case for minor chords).
Continuing in this way, we get the following diatonic (meaning: derived from the same key) chords:
This way of understanding harmony is tremendously helpful to guitarists in particular. We play an instrument that makes it really easy to transpose chords---you just move the shape up or down the neck to the appropriate fret. All the chord shapes work the same way. Here are two examples to illustrate the point:
Example 1: Pick a key, any key---how about, say, Bb. The notes in the Bb scale are Bb, C, D, Eb, F, G, A. The sixth note is G, so if I build a chord on G, but staying within the key of Bb (i.e. using only notes from the Bb Major scale), I'll get a G Min7. I don't even have to think about what notes go into that chord or what the intervals are; because it's the vi chord, it's a minor 7th, guaranteed. So when I'm playing in the key of Bb and the chord progression calls for a vi chord, all I have to do is find a G and use one of my Minor 7th chord shapes.
Example 2: Imagine I'm on stage and the bandleader says "Rhythm Changes in Eb: 1, 2, 1 2 3 4" and we're off. No problem. I don't have to figure out all the notes to every chord, because I know that the numbers for Rhythm Changes are I - vi - ii - V, etc., so I already know that means a Major 7th, Minor 7th, Minor 7th, Dominant 7th. All I have to figure out are what the root notes of those chords are for the key of Eb (in case you're wondering: Eb, C, F, Bb) and use the appropriate chord shapes. Also, because all of those chords are diatonic, I know that any notes in the Eb scale will sound good over all of them, so when it comes time for my solo, I find an Eb scale on the guitar and go to town.
The 1-6-2-5 progression is, well, the I – vi – ii – V progression! In C major, that would be C – a – d – G. In G major, it would be G – e – a – D. It's native to the diatonic major scale, but it certainly works across a number of scales (with modification in some cases). This progression is also the foundation of the turnaround in blues.
It could be a progression:
I iii V VII CM Em GM Bdim
Then you could work within CMaj scale and do modes over each chord.