Today we've released UTM 9.508. The release will be rolled out in phases. In phase 1 you can download the update package from our FTP server, in phase 2 we will spread it via our Up2Date servers.
As part of UTM 9.508, the wireless firmware is updated to 11.0.003.
Researching the upgrade path from 9.506-2 to 9.508-10 to see what problems to expect and would love a fill in on the MTU issue described here. You can change the MTU setting in interfaces, so not sure what you are referring to. If there is an issue with MTU directly impacting web browsing then I could very well be suffering from the same issue.
I have noticed that our UTM performs better for browsing sites after a reboot, so much so that I scheduled a reboot to occur every night. Even had users compliment how fast the internet was when they were not aware that I had implemented the workaround. A single HTTP file download such as speed test will be fine, however browsing is sluggish and times out - gets worse over time. There is definitely an issue with an underlying service somewhere, and it has existed for a long time.
I will be remote upgrading our UTM so want to avoid having to reimage the system as much as possible.