Last night I've tested iNav iGuidance 2009 on my touch pro and I'm sad to inform you that has the same lag as Garmin Mobile XT (3-5 sec.). On the top of that I had to use tweak to start this app with gps since iGuidance ( same as prev. ver.) is not recognizing build-in gps.
So far from all gps apps I've used ( tomtom , iguidance 4, 09, garmin XT, igo
IGo8 is my favorite one with fast screen refresh and almost no lag while driving.