Don't listen to the BS about commercial being immune. Commercial is at a top. I won't say it is as vulnerable as residential, because you're dealing with long term leases, but regarding anything other than triple AAA tenants in great physical locations, commercial properties are vulnerable to an economic downturn, too. And remember, commercial follows rooftops.
"IF" commercial real estate is at a top which I think it may soon be, it would be good to pay attention to SRS. Trading around 79-80, pointed it out on the other forum around 66 a share when IYR was flying high above 90+. Commercial Real Estate cannot stay hot forever.