Soakedlontra,
I, like many of the others on this forum, have dove this site quite often and it's one of my south sound favorites. I've dove it from my boat, dive charters and from shore. Haven't dove it for a while now that the boat is moored up in the San Juans though. (Now I'm spoiled).
IMOpinion, diving at slack is always best - little to no current.
At this site the shore enterance/exit is north of the best part of the dive. Problem is that some of the home owners don't like divers walking on "Their" beach so rather than ruffle feathers we usually make the swim or do the boat.
If from shore I like slack at highwater. It can make for a deeper dive but I like having the current with me both to the site and then back to the exit site. At low slack, I usually dive at 70' so at high slack it'd be about 14' deeper. I don't use much air so it's not a biggie for me.
From the boat you don't have to worry about the swim so I always go at low slack.
As far as the dive books recommendation of doing it at a 8 foot exchange, I believe what they are trying to say is that viz is best when there is minimum water running through the area. I've dove it with 15' changes and 10' changes and while the viz may be better at a 10' change, it's nothing compared to a good old summertime alga bloom.
PS, good spot for octos - and enjoy the dive.