B-site ordered double perovksites comprise a potentially large class of frustrated magnets but have, until recently, been relatively little studied. Diffuse magnetic scattering will be measured in two B-site ordered double perovskites,Ba2YRuO6 and Ba2YReO6, which are highly frustrated, f ~ 14-16, antiferromagnets with very different ground states. Ba2YRuO6 shows long range Type I fcc order below 36K but diffuse magnetic scattering is detectable above 50K. Ba2YReO6 shows a complex two component spin freezing with anomalies at 45K and 20K but no long range order. The obtained Smag(Q) will be modeled to measure and separate the contributions from nn and nnn super-super exchange for both materials.