Heighten:
Warlock: I would want to use heighten spell on eldritch blast, being able to blast your enemies 90M seems fun as all hell
You want the
Eldritch Spear invocation, which Larian haven't put in game yet.
But you're thinking too small. After taking Eldritch Spear, you can mod in the feat for metamagic, and use distant spell to double that range to 600 feet.
