It sounds like your options are pretty limited. Fast growing trees are going to get really big. Most fast growing trees also end up being weak-wooded and short lived. 'Green Giant' thujas grow quickly and have far few problems than Leyland cypresses (which I would definitely NOT recommend), but the Green Giants are going to get pretty large eventually (and very possibly much larger than you'd want). You may want to consider a vine-covered fence or even a hardy type of bamboo with a root barrier.

Hi Bruce thanks so much! This is basically a companion plant for a Quick Fire. I was thinking about a Ninebark for the purple...I think I want some purple! I have a 'Baby Blue Eyes' and a Black Hills Spruce paired up on the other side of this plant, and I could be interested in a conifer, but I'm not sure what would not get so big and look good with the pink of the Quick Fire. Which is why I was leaning toward purple, and the nine bark might be great. I was thinking Summer Wine for the disease resistance, but it isn't supposed to get that tall and don't nine barks generally need to be hacked down every few years to get them to grow nicely? That's why they weren't on my top list. The Seibold is interesting. I have a Nannyberry and three other viburnums that my builder installed so pollination shouldn't be an issue!

@Fori -Thanks so much, I think that is a great solution for the bay area. I think we may end up going that route :) All of the fences in our neighborhood are supposed to be 6 ft but somehow most seem to be 8 or even 10 :) I was reticent to ask, because we get along really well and I didn't want to make them feel pressured to do something to the shared fence that they didn't want to, but I think that is probably the best idea!

The feeling of privacy is different from whether or not you can be seen. My city back yard feels incredibly private and many people remark on that. I have 2 pieces of lattice in the least-private part of my yard, which makes a huge difference. We also installed an inexpensive metal gazebo on our deck, with a fabric roof that comes off in winter. It only cost about $200. We don't need the shade from the roof but what we do need is the feeling of privacy it gives us.