You are simply thinking it the wrong way, you have to know the outcome before calculating:
The outcome has to be: You at your new level (1000' separation) at a safe distance (lateral separation, usually 5nm)!
Knowing this, you can throw in your speed, your climb performance, winds, etc to get a minimum rate to do this safely. That is how you will fly it then...
Nic
PS: aren't the vx and vy marks (blue- and redline) on the speedscale for single engine