Indeed, Monty's pursuit could perhaps have happened faster, but if he had advanced faster, he risked several things;
1. Large casualties in the minefields the Germans left behind again and again and again.
2. Running out of supplies and exposing the troops to a German counter-attack.
3. Running ahead of support (air, artillery, infantry) and thus exposing the troops to a German counter-attack.
With Torch happening, Montgomery knew that the Germans in Africa were doomed. He wanted to preserve his forces as a coherent fighting force to make sure Rommel could not rebound like had twice before.
Husky could hardly happen sooner anyway - Rommel's El Alamein part of the forces in Tunisia was rather low.
As for 4 divisions 1940, the infrastructure in Libya cannot support it. Rommel did a lot of his advances in captured British supplies. Once that source ran out, he was unable to supply his troops, as happened before Crusader and before El Alamein.