800xA 5.0 SP2 base software and Rev A can be installed at Windows 7
Yes there is impact of windows version on 800xA. Please refer to supported operating systems section in the installation manual.
Even if it looks like 50sp2 RevE is working on windows 7 64 bit, it is not a supported OS for that version of 800xA (and most probably not tested too).
You may end up in not getting help from supportline if your OS is not supported.
Contact support line for more information.