Any thoughts on the importance of transconductance tests when testing tubes?

[old_tv_nut]

Haven't thought about TV apps in particular, but it seems to me transconductance might be more critical for high gain stages like the typical luminance output stage in tube color sets. I know different video output tubes that all tested OK for emissions made noticeable differences in video drive in the Magnavox I had, so might be the difference was transconductance.