The way I read the two is Spell Combat is what allows the Magus to cast a spell and attack with a weapon (with penalities) in the same turn as a full attack.
Spellstrike on the other hand allows the Magus to cast the spell and "deliver the spell through ANY weapon as part of the melee attack".
So Spell Combat allows for the casting of the spell during my full round of actions, then the Spellstrike allows it to be one melee attack roll to deliver the damage of both the weapon and the spell (I am figuring I still have to take the -4 on the melee attack roll)