so… (
Safe Harbor…We are doing stuff with DMT and UpdateEXT in a future release… and we did find something!
During some changes that we are doing in DMT, we are changing it to be more efficient, and instead of adding/updating/deleting one record at a time, we are going to be sending larger blocks of data (also know as "page size)…
What we found was that, while we are going to make this be a flexible setting, a page size of 200-300 maximum was the most efficient, and we saw a huge improvement as compared to doing it one record at a time. We also put a high end limit on page size dut to exactly what you have found.
Also, Updatable BAQs use UpdateEXT, so, same rule above would apply.
So, you might try changing how many records that you push to an update at a time (if possible in your code) to see if it more efficient by only updating 200 instead of 900.