LOL...I wish I could muster a pathetic 8min pace. I am usually closer to 9 on the run.
That being said, unless you are looking for podium times, a tri-bike won't matter that much. From what I have read, bigger gains can be had in transition. I was looking to get into one for all my rides as I have friends that have made that transition. However, now, I am looking at some of the aero-road bikes like the new Fuji Transonic.
I suppose if I was only going to do triathlon, I would consider it more.