Speed rating on tires - question

I've had my 2004 Civic LX for a few days now and I really like it. I do have one concern, however. The dealer replaced the original Firestone tires
with Bridgestone Insignia's, which I know are low end OEM-type tires. My concern is that these tires are S-rated, but my manual says that H-rated tires are recommended for the LX model (S is acceptable for the base DX).
I know that the maximum speed capability for an S-rated tire is 180km/h (112mph). Because I never approach anywhere near that speed, I figure the S-rated tires should be OK on my LX, notwithstanding that they probably won't last long with all the driving I have been doing as of late. But what I would like to know is if I could use a Q-rated winter tire on the car during the winter months, or if this is too big of a drop from the recommended H.
Thanks in advance.
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