I am aware that you cannot upgrade a silver sword, but it is possible to find one that doesn't svck? I'm a level 40-something on Xbox 360 but the greatswords I find have like 34 damage or something.
Smithing =
Daedric Greatsword,
Enchanting =
High Smithing Enchants on Equipment.
High Smithing Enchants + Daedric Greatsword = High Damaging Greatsword.
My own Daedric Greatsword has an enchant on it for Fire damage and the smithing enchants I had on my armour while I upgraded the sword..
made it do a smooth 100+ Damage for each hit, +20 for Fire damage.
Edit: Given your level and build I'm suprised you're still using Silver and not Daedric-Ebony already. & There is no way to make a Silver Greatsword not svck, sorry. :/