Hahaha..oh boy...tall task amigo!
I think the best way to do this is break things down by the player, having already done Fletcher. It won't be great, because frankly I've had a couple and am a bit tired, but screw it let's give it a shot.
Spikes is a Mike (middle linebacker) regardless of scheme. He doesn't have the footspeed and fluidity to matchup in man, but he understands zones and angles extremely well to create deceptive speed. His reads and playing style are pretty unorthodox, but they are often correct. He seems to have the best hip explosion on the team, and is the best hitter in the group. He disengages as well as Mayo, and has as good a burst as anyone on the team. This, combined with his ability to read so well creates deceptive playing speed that makes him a tremendous hash to hash player. A sideline to sideline player he will never be.
I think that Mayo is a Will (weakside linebacker) regardless of scheme. The Will in the 43 and 34 are a bit different. The Will in the 43 plays as the weakside OLB, and in the 34 as the weakside ILB. The Will in the 43 is a coverage/contain/pursuit player, whereas the Will in the 34 is your playmaker. Mayo is best in pursuit, but is a capable player in stoning the momentum of blockers and disengaging. He bring 43 Will speed to a 34 ILB frame and that is a rare mix. As a career linebacker, I think he lacks some of the timing required to blitz at a high level, and that surprises me a bit. He is still developing, but his quickness, knowledge of scheme, understanding of angles, and knowledge of disengage moves are impressive for a 4th year pro.