what length is the rod ?
I fish a 510 Airflo compact or an SA extreme 520 on my 12'7" 7/8wt spey. I would be fishing the SA but my dad borrowed it to try out and refuses to give it back now because he likes it WAY more than the Rio Flight(525) he was using on his 8126
ok i did a quick google search
is your rod the Echo DH 13'3" 8wt ? if so it says the grain window is 540-660 for that rod.
OR
is your rod the Flylogic Dec Hogan signature series 1308 rod ? all i could find is lines in the 7/8/9 wt ranges perform the best which should put you in the 550grain area + or - to the way you like if of course.
I tried out a 540 on my same rod and even though it cast great it felt heavy when i really got a perfect cast and would go out a bit clunky, tried out a 510 and 480. 480 didnt want to perform sustained anchors very well but did airborne casts wonderfully. the 510 did them all with ease and didnt crash when it laid upon the water
go into an ACTUAL fly fishing store and ask if they sign out shooting heads. get a few and hit some water close-by and test them all out. buy the one that feels the best. i did this when i had my switch rod, i probably tested several grain weights from a few different companies to find the fit i wanted.
this is all part of the fun of the two handed game.............Enjoy