Upgrades should always be consistent when considered relatively based on your smithing skill and bonuses from enchantments or potions. Skyforge steel will upgrade more than regular steel because it starts with a higher damage base than a regular steel weapon. However, upgrading it will not make it come close to a higher damage base weapon also upgraded under the same circumstances.
For example if the base on a steel dagger is 5, the base on a skyforge steel dagger is 8 and the base on an ebony dagger is 11, then when all 3 are upgraded the Skyforge will of course receive a bigger boost than the steel, but the ebony will receive an even bigger boost than the Skyforge.
This is as I said with all circumstances being equal. If you have the steel smithing perk and not the ebony smithing perk however, then the circumstances are not equal. Your steel (including Skyforge steel) weapons will see a bigger relative increase.