Different people say different things.
For my Tier 1s, I have developed some sites that are actually OK.
Each is a real site. By that I mean no nonsense, and some even get real traffic.
I'm not necessarily hiding that they are connected,either. Not advertising it, but onmce in a while they do link to one another in a semantically-meaningful way when appropriate. They aren't PBNs that are like fake stage sets. lol
Does it matter if more than one such quality Tier 1 domain has same C-Class, or even entire IP address?
I have many other links pointing in as T1 links from other places, so overall, there is diversity in IP addresses, but to save funds, I put a few different (quality) T1s on the same hosting accounts.
Please let me know what you think, GSA pplz. This is another area I expect I'll get some opposing answers!~