GP posting slow with Extender
I have seen large amounts of Extender data cause performance hits before. There are a few different options that I have come up with.
1. Create a historical company and move the history to that company.
2. You can try removing the blank records and see what happens. This would need to be tested in each environment as it depends on what your window setup is as to how it is going to react to the data not being in the table.
3. Sometimes the window can be changed so that the data is stored differently such as only using strings when they are truly needed, making the sure the keys are necessary, etc. The only thing with this is that depending on the change, the data needs to be taken into account and may need to be exported and imported to be able to keep it.
4. Extender in GP 2013 changes the way the table structure is done, so it should be faster in 2013, so updating would be an option if you aren't on 2013.