How much you have to "zoom with your feet" (walk) depends on the distance to your subject. The FoV (field of view) varies with the inverse of the focal lenght (for a given camera), so going from 70 to 200 mm focal length means that your FoV becomes about a third. So your subject will appear about 3x larger in the image. To get the same effect by walking, you'd have to reduce the distance to a third of the original.
But there is a big difference between changing the focal lenght and changing the distance.
Changing the focal lenght doesn't change the perspective, so the relative sizes of items in your image stay the same when you zoom.
When you walk closer to your subject, items that are farther away will appear smaller compared to your subject. So you change the relative sizes of the items in your image.
You can test this easily enough with your 24-70: take 3 pictures: one at 70 mm, then one at 24 mm where you stay in the same spot, and one at 24 mm where you approach your subject to get it the same size as in the 70 mm image. Now, enlarge a copy of the first 24 mm image so that your subject is the same size as in the 70mm image, and crop to the same size as the others. Now compare those 4 images.
If you also want to compare the Depth of Field, make sure you stay pretty close to your subject, and use F2.8 (at 24mm, your depth of field can eadily go to infinity at larger distances, especially when stopped down to F5.6 or higher, see below for a link).
Usig a DoF (Depth of field) calculator for F5.6 gives the following:
70mm @ 10m : DoF ~ 3.5 m,
200mm @ 30m : DoF ~ 3.8 m, @ 10 m : DoF ~ 0.5 m
So with approximately the same subject size, DoF is about the same, at a given focussing distance, the longer focal lenght has a much smaller DoF.