We upgraded part of our farm begin this week without issues and last night we upgraded the vmtools on 4 of our exchange servers. Unfortunately the backup speed has since then dropped from 2040 MB/min to 1375 MB/Min.
We're about to check with our template if installation of the upgraded vmtools is responsible for this drop in speed.
Well, first trails with netperf show no drop in network performance after installation of the 43424 build of the vmtools. A closer look at the backup logs showed that there are differences in backup speed per store which leads me to think it is unrelated to the vmtools update.
We'll see what happens with the backup speed tonight.