@Antvasima
In the 25 years of Post-Crisis Speedster history, Wally's interaction with the Semi-beaten Anti-Monitor in Flash Vol 2 #150 would be the highest non-speed force tapped feat at At least
2-C/2-A (See Anti-Monitor pending CRT). I consider this an outlier.
Flash has consistently shown that his heaviest attacks on his own rely on relativity. In the same Chain Lightning Storyline Flash Vol 2 #148, Wally describes his Dwarf Star RMP as his hardest punch ever, going all out because of time travel logic. Ripping the universe via his IMP at exactly the speed of light would be
High 3-A/3-A since nothing implies it destroying the timeline or affecting time.
As for feats tapping into the speed force, we have Wally defeating Cobalt Blue, Bart Allen volunteered to absorb the entire Speed Force so that he would be fast enough to stop Prime, and Barry traveling back in time to save his mom causing the Flashpoint Timeline. I would rate their use of the Speed force in this era as
2-C.
The multiverse map wasn't introduced until Multiversity in 2014, so we shouldn't apply that structure to past stories and feats.