I have very similar issues, and posted about them
here yesterday. I've been pulling my hair out trying to get this to work smoothly.
Does anyone happen to have the same problems in the main menu when disabling the RSS feed? If I put the FPS counter on, and disable RSS, the FPS will drop to anywhere between 25-45 fps while idle on any selection on the main menu. Then if changing selection during 3+ second idle, it will "stutter" onto the next one. If I move from one selection to the next quickly the FPS will stabilize and will change selections very smoothly. The odd thing here is that on my desktop PC the FPS will still drop, but I won't get that same "stutter" that I do on my HTPC.
When you guys say that it's locked at 60fps... is it completely locked with no variation at all? (exactly 60.0 or 59.9 fps while navigating wall views?)
Desktop = i7 2600, nvidia 560ti, 8GB ram, SSD. Windows 8 x64. Library on local hard drives.
HTPC = i5 3570k, nvidia gt630, 8GB ram, SSD. Windows 8 x64. Accessing library through SMB from desktop. No path substitution whatsoever.