This. Around 2.8Ghz core and 16GB ram are standard for us. Occasionally we have to settle for 8GB if that is what all that is available in Apple refurbs.
I don't care about CPU speed very much, but yeah, 16GB at least for a dev machine. You need something you can run a database on, perhaps an http server + framework, etc.
Virtual machines are a killer too. We are primarily web but end up doing more than our fair share of legacy WinForm app updates and that requires a lot of ram if you're going to have at least somewhat of a pleasant experience in VS inside the VM.