reading some of the threads of late and it would seem some are riding around with 2 1/2ft plus of tubing laced through their stem.
i've recently fitted 690mm having had 640mm. i've really noticed the extra 2.5cm either end. it helps open up the bike and adds more stabilty on techy bits.
where are you riding because i've found more than one 'bite' point on the local wooded single track.....? open moor land?