Thanks for the suggestions. I may just stick with the EKG (mine are currently 5.6%), though I do have a pound of Challenger at 7% and love the hop in just about every way (including a SMaSH bitter). I don't know that I've ever used Cluster. Is there some rep of this very thing we're talking about, that some find Cluster a bit "harsh" or "unclean" in bitterness quality?
For a while I was doing Challenger/EKG pales and Cluster/Fuggle milds, stouts, etc. No scientific method there, just felt like the thing to do. Then I hit on a batch of grapefruity EKG and I went off it for a bit. Northern_Brewer has commented on it. Something about particular year's weather. My most recent bag of EKG wasn't grapefruity, but it was only ~4.3% if I recall.
I'd stick to your EKG and see how it goes.