Although its not much of a solution, try using an app called "Call Confirm". This is a must have for my Eris. I am rooted and running xtrsense, which I love, and is definitely fast, but I still get lag when dialing and connecting calls. This brings up a window which asks you to confirm that that you want to call the selected #. It doesn't stop the lag, but it does prevent "double" dialing by accident. Once the confirm window shows up, you know that your phone is "ready" to connect the call.
I'm not sure if its the HTC smart dialer or the eris itself, but dialer lag seems unavoidable with this phone. I've tried several ROMs and they all seem to fix it at 1st, but it always seems to creep back eventually. I guess I've gotten used to it by now, but "Call Confirm" has made it considerably more tolerable. Hope this helps!