I agree with BMSF on this. He and I are about the same height.

I am 5'10" and ride a 54 cm road bike. I looked at the Sirrus on the Specialized website. It looks to me like a road bike with flat bars, not a mountain bike. It's hard to tell about the frame size. One website listed sizes as small, medium, large, etc. so that isn't helpful. You can see all the different models on Specialized's website.

One question is how was the 54 cm measured? The usual way to measure frame size is along the seat tube, however, it could be center to center (center of crank to center of where the top tube meets the seat tube) or center to top of the tube (meaning the frame is smaller if measured center to top). Mine is center to top, which I suspect is more common. 54 cm = 21.25 in. if you don't have a metric tape measure.

In any case, 54 cm will probably work for you-adjusting the seat post will make up for any slight discrepancy in exact size. Aluminum frames are pretty comfortable if you haven't owned one before. The exception in my opinion - the big diameter frames like Cannondale-I had one and it was so stiff I got rid of the bike after a few months.

Specialized makes nice bikes. I have had two and still have one of them.

If you decide to get a mountain bike, frame sizing is different than road bikes. I have a 19" Rockhopper and it is too big for me. It should really be a 17" frame for off roading, but it is fine for around the neighborhood. Sprung forks add more to the height of the bike than I thought.

As far as the China question, the answer is probably yes. US made frames that I have seen are usually from small manufacturers and very expensive. Even bikes with European names are now made in Asia.

My Rockhopper just says "Designed in California" which doesn't mean much. Apparently (I did a quick online search) the frames are made in either mainland China or Taiwan. Not sure how reliable that info is, but sounds right.