The difference is that 11.5.3700.0 is the version of the assembly (this never changes from SP to SP). And 11.5.9708.826 is the file version. This changes from SP to SP. This is normal for all assemblies.
What bothers me is that as far as I know, SP 6 is supposed to have a version of 11.5.12.1838. Where version 11.5.9708.826 came from, I have no idea(?). You?
It may be worthwhile to try and run the SP 6 update in any case and see what that does. See this blog on how to.
- Ludek