Any time between June and August is cool with me..
I don't post on the Russia forums much, but live in SVO during summer and go over a couple times a year.
And yes, IAH-MOW for $600 is a great deal. Is that on the new SIA non-stop? Moscow is sort of expensive if you don't know the right places to go.. but definitely nice in March and April. It starts thawing out and warming up.