I use the 720i HD option. Can't remember if that's exactly it?? Then scale it down after I bring it into my SD sequence. I think Tom's way is better. Font size is tricky when you start working across codecs.
I had to bang out about 20 titles the other day and had just this problem. I'd never used LiveType before but it was pretty easy after I got going. I'd been given a short example of a video that had been edited on an Avid so I could emulate the titles and transitions in FCP. I worked quite hard at making my piece look like the example. A couple of days later the producer says they like my look better so they're going with it??! Not sure weather I should smile or cringe? At any rate, they're going back to the drawing board with the Avid cut stuff to see if they can juice up the titles a bit (haha.)