Here is the calcs for a Lv. 100 Metagross' Hammer Arm versus a Lv. 100 Tyranitar:
252+ Atk Metagross Hammer Arm vs. 4 HP / 0 Def Tyranitar: 452-536 (132.1 - 156.7%) -- guaranteed OHKO
Here is the calcs for a Lv. 50 Metagross' Hammer Arm versus a Lv. 100 Tyranitar:
252+ Atk Metagross Hammer Arm vs. 4 HP / 0 Def Tyranitar: 240-284 (136.3 - 161.3%) -- guaranteed OHKO
As the calculations show, the damage difference between two identical Pokémon levels 50 and 100 is virtually nil. There is a 5% difference between two nearly identical layouts. This leads us to conclude that the damage output at Lv. 50 is simply the same as the damage output at Lv. 100. The reason Little Cup Pokémon need so many EVs is because they are Lv. 5, meaning that they can take advantage of complicated spreads better than their higher-tier counterparts.
Here are some further calcs to demonstrate the level 50/100 damage correletions:
Porygon-Z vs. Rotom-Mow: Level 100
252+ SpA Choice Specs Adaptability Porygon-Z Tri Attack vs. 0 HP / 4 SpD Rotom-C: 278-328 (115.3 - 136%) -- guaranteed OHKO
Porygon-Z vs. Rotom-Mow: Level 50
252+ SpA Choice Specs Adaptability Porygon-Z Tri Attack vs. 0 HP / 4 SpD Rotom-C: 146-172 (116.8 - 137.6%) -- guaranteed OHKO
Palkia vs. Kyogre: Level 100
252 SpA Palkia Thunder vs. 4 HP / 0 SpD Kyogre: 200-236 (58.4 - 69%) -- guaranteed 2HKO
Palkia vs. Kyogre: Level 50
252 SpA Palkia Thunder vs. 4 HP / 0 SpD Kyogre: 106-126 (60.2 - 71.5%) -- guaranteed 2HKO
To calculate more, use the Smogon Damage Calculator and set the levels to 50.