I've done this in NY, LA, SF, and the suburbs. (I moved 10 times in 10 years.)

I don't say this out of inexperience.

Feel free to take the lane and put your life at risk otherwise if you disbelieve me. You hold up a car for over 10 seconds, and they'll honk you or squeeze you off to the side. Every time. Do it in rush hour and they'll try and crush you to squeeze by. This literally happend nearly every single time I did it - at least 50 times on various roads in various cities when I was investigating bike commute options. In NY, LA, SF, there are enough roads where you have to 'take the lane', and if it's more than trivially short, forget about it.

I'm also a experienced road cyclist, and have no problems asserting myself. But trust me - you take a lane for over 10 seconds, and you're going to get honked or squeezed. Sometimes that is the only way for that day, but it's far better to find a better route that at least has a side out. I have had no problems with extensive road training and road commuting, even if the busiest parts of LA (around UCLA) when the routes were chosen correctly, even at rush hour.