While I'm sympathetic to the drive to have The Best Players eVar, I'd let it go. You already have two world-class potential QBs on your roster, and you won't be able to afford both in the long haul.
As a GM, I'd pick the horse you want to ride from among those you have and ride him until it's time to replace. For example, in three years I moved from ARodg to Andre Woodson to Jake Scott with my Packers franchise, and I never started a rookie or rebuilt a starter's playbook knowledge from scratch (after year 1, that is). Mastery is worth having.
If you can trade for English without losing your current starter, I'd consider it, but even the game-Raiders might not be that dumb.
Alternately, consider drafting or trading for Darius Pryor to develop as your Next Great QB. He's got plenty of tools.