Hi,
No issues with W7-64 bit, and I added it to a second computer which was gifted to my friend (after an upgrade!!!), and a bit later had an issue with the video card (GTX650). I took the opportunity at the time to upgrade the memory on the computer so my friend had a reasonable one to play with.
The main issue was that W7-64bit, did not like the current (at the time) video driver for the card and any games would crash after 5 minutes, and this was resolved a bit later by upgrading the video driver.
Other than that, no issues, other than the validating BS ...