Dennis, Go ya halves in an 800mm F8L
Yeah, longer lenses are all the go... especially quality ones. then you can mount them up on your EQ6 and have a bunch mini-ultra-flat-field APO's..
70-200 F/4L is a great starting 'long' lens, priced well, good focal range for a wide variety of shots, sharp as hell..
Once you look at the 300 prime's and bigger your starting to look at rather specialized lenses, that are only good for a few subjects... birds/sports/astronomy... but lets face it... Everyone.. I mean EVERYONE!! wants a 600mm F/4L