Hmm.... I have a team of 5 pallies with epic fliers, and with crusader aura perma-enabled, I usually never have problems. I have all my graphic options dialed down to the lowest except for particle effects at medium and viewing distance set at medium though, so not sure if that's a factor.

I'm running vista x 64 with 8 gigs of DDR2 ram. ATI 4870. C2Q 6600. all 5 wow are symlinked also.

The only thing that gives me trouble is the phased areas in icecrown. But when I know I'm about to go through one of those areas, I'll just line up all my followers with the leader by having them autofollow for 2 seconds then stop. I also have auto-run mapped to a key on all 5 instances, and I will hit that key. Since all 5 are lined up exactly after auto following for a few seconds, they will all head in exactly the same direction upon hitting the auto-run key. When I get close to where I want to go I will hit the auto-follow focus key again and then since they're all traveling in the same cluster at the same speed, I never lose them that way.

Sorry if my explanation is convoluted, not enough sleep.