Safebet:
I have this plane and have been flying it for over 2 years. I have heard a lot of discussion about washout and tip stall, and in fact, I was bit by the tip stall bug once. I ended up needing to rebuild.

With that said I don't have washout in mine and don't want it. You should evaluate what you want your plane to be and how you expect it to fly. Do you want a full-blown aerobatic machine that will knife edge and fly inverted? How about snap rolls? If the answer is yes, then leave out the washout. In order to snap roll you need to induce a tip stall and washout will fight that. It will also cause bias in inverted and knife edge flight. If on the contrary, you want a gentle airplane with a more predictable stall then add the washout.

It's really as simple as that. You gain some things with the washout and you loose others.