Early in that timeline Solaris was heavily into being a "pure" System V r4. The pipes and sockets implementations were based on System V Streams -- the in joke was that streams were much more like sewers and they weren't pleasant. Numbers wise, they were perhaps 2 orders of magnitude slower than on SunOS (BSD based). At one state university, where a very "beefy" SPARCcenter 2000 was purchased to support 500 simultaneous users, Solaris on this system could barely support 40 users (streams performance was the reason - telnet sessions pushed several streams modules). Sun ended up having to provide 10 SPARCstation 10 systems running SunOS which could easily support 70 simultaneous users each in order to fulfill the contractual obligations. The SPARCcenter 2000 was turned into an NFS file server.

After the early days, Solaris did improve, but I think that was because ideas / pieces of BSD (from SunOS) were put back into the OS.

I don't think Solaris pipes / sockets performed better than Mach.