Sophos has a huge user-base, double its nearest competitor in the enterprise web security space, and thus they find out about a lot more than say a startup that might have less of a resource-drain than they might have. However, that said, Sophos 10 is said to not be as much of a CPU hog than 9.5 even was.
They're always working on those things at major software providers, to ensure the best experience for all users.
Sophos has a great track record with antivirus solutions, and I understand that they do not publish reports about everything they find to VirusTotal but that doesn't mean they didn't trap the virus either. Found that out when I reported three new ones received in spam earlier this year.
They also have a great web content filtering solution I wish we were using, again the huge user base probably helps with that. Our current solution has a very small user base so they will probably be missing many bad sites, even with dynamic scanning of the content on the page, although something is better than nothing, I really wish we had the Sophos web filter too on top of anything else the Church uses to block all the garbage out there, including whatever the other filter will miss, it's that important from a security standpoint as well as any other reason one has to use a content filter in the enterprise.