You may also get lucky with a 3770K in regards to you get a chip that likes to cooperate, since every batch is not the same. This one may not get this frequency and good temperatures, but that other one may.
If you want the very high over clock of 5GHz, the 2700K is the way to go. If you're doing minimal overcooking, and want a tad bit higher performance stock, I'd go with the 3770K. The 3770K generally seems to get to get to 4.7GHz, or in that range.
Both with good aftermarket coolers though. The 3770K does consume a tad bit less power, but runs hotter under load overall. I can't recall if it runs the same temperature at idle however.