for the straight there are other factors
1. westerly swell vs wind waves
2. southerly wind vs ebb tides in rosario straight
i went across for 4th of July. there was Gale warning in the straight so went up the backside of whidbey. I timed it right to give me the option for a deception pass run on the tides but last minute chose the swinomish channel route as a gale westerly on any ebb current coming out of deception pass is very ugly.
good thing I did the channel as the straight was fogged in as well as windy.
its about 3 hours to 3:30 from elliot bay to La conner/deception pass at 15 -18 knots. if you go through deception pass its a total run of 5 hours to Roche harbor. if you go via swinomish channel, guemes channel, thatcher pass its 6 hours from elliot bay to Roche.
if you go straight across the straight you cut the time to 4:30.
if its even remotely bad weather go the long way; its way more pleasant and very easy to go up the swinomish channel. evne stop for lunch in La conner 🙂
the other thing to watch is ebb tide in rosario straight. it can get pretty lumpy beam seas if going the channel route just plan for slack in rosario and its super easy.