I quote from a recent remark by Jeff Hobbs, Senior Developer at ActiveState: "That's a classic misconception that people have with Tcl. It is so much faster than most people 'remember' it being, as they all worked with the pre-on-the-fly-compiler version. Tcl 8.0 changed the rules and 8.4 pushed them again.
You can see version speed differences at http://wiki.tcl.tk/1611. In the simple case of list iteration (#255), 8.4 is more than 240x faster than 7.6!"