Which set to use depends on the height you need to reach. The AF set might not take you up high enough to go over Lionels without extras piers with shims on or under them. (also, some lionel equipment needs up to 7¾" overhead clearance nearly 2" taller than the tressels. "Cement" footing shims of painted 2x4s is what most folk with 6"+ needs use to rise more.
The grade is a % of rise vs run that doesn't change with scale used. The track lengths however move the intended spacing of piers at joints and that does change the grade.
PW Lionels have a steep grade over 4% with 8¾" tracks. You really want two sets per grade with 1/8 shims under one set to get nearer 2% . (hardboard wall paneling is about the right thickness)
Lionel tracks were 8¾" long for 0-27, 10"-O, and 9" Super O. Each had a slightly different grade when using the same tressels, O% was lowest.
If tressels on an el, are firmly attached to the layout kinda near each other so two in a curve are at a 90° to each other , this little bit of cross bracing does wonders for lateral stability of a whole loop. Half of mine are only connected to the track and the other footings just sit there relying on the 90′ pairs to sure it up from any movement. (It will seem rickity like dominoes until you get 1 90° bracing pair done and or secure track to gound level . (you might not be doing a loop, but the general principal will be understood once you begin imo)
