Folks,
Vx and Vy are determined by excess power vs EAS.
I have a neat diagram, but can't insert it (sigh!) - but look at Figure 91 in Preston:
http://selair.selkirk.ca/Training/Ae...l%20pilots.pdf
I'm with Bloggs on this. If you fly off speed either way, your air mass-referenced gradient reduces. If you are now earth-referenced and increase your EAS, you will increase your groundspeed and amplify your gradient reduction. If you do it downwind, it's an even more dramatic reduction in gradient. Between you and me and the gate post Hazlenuts, that is not how I plan to clear obstacles!
Stay Alive