I have these in piano black as well, 3x for my LCR. Amazing speakers.
When I got them 3~ ish months ago, I was experimenting with setup and I found I could toe them out quite a bit and maintain a solid center image (maybe 30 degrees away from LP). However later on I pointed them back inwards a little more, like towards my shoulders or slightly wider (maybe 10 degrees from LP), and compared listening to some Norah Jones tracks. I noticed that her voice lost some of the higher mid/treble timbre when toed out further, and regained when I toed back in. I've kept them with the closer toe-in angle since then.
I posted my initial thoughts and pictures here in June:
I've done some REW testing on them. I'm moving in a few weeks and planning on adding a sub (maybe Rythmik F12SE for FVX12), looking forward to having fun setting up and measuring them in the new house.
I think Erinsaudiocorner is going to be measuring and reviewing the Sierra-LX's soon, according to a response he made to a comment of mine on one of his YouTube videos recently.