I honestly could not say if MS SQL Server performance is better or worse than its competitors, but I feel confident in saying that the differences are not so great that any could be said to be "wiping the floor" with the other. For a start, fair comparisons between different databases are pretty hard to set up.
I think Robert Haas who is chief architect for Postgres put it best in a blog post response to someone asking him about SQL Server vs. Postgres performance. I've dug it out for you. (Caveat: I am a major postgres fan).
http://blogs.enterprisedb.com/2010/12/20/postgresql-performance-vs-microsoft-sql-server/
It's only short and worth reading (imo), but for those who can't be bothered here is a paragraph from the end:
I think the important thing to realize here is that both PostgreSQL and Microsoft SQL Server are complex, robust products with many features and generally good performance. People can and do use both products to manage large amounts of data in critical production environments. It would be a serious mistake to believe any categorical statement about which system is faster and by how much. There are going to be cases – in either system – where things just don’t perform well.
He is a very, very smart person.