Are we talking about 17" steel wheels or the alloys? My SR5 came with the 17s, but they were the alloy wheels, and the option (port install) was more like $450., not 100)!! I would imagine that it would be hard to find an SR5 with out the alloys. I looked at 25-30 in my area, and none had the 16" OEM steel wheels. As for the difference in ride quality, I think (IMHO), that is more of a subjective thing. I ordered a set of OEM 16" steels for winter use, and have 275/70/16 REVOs on them, and it seems to me that ride softness is about the same when compared to the 265/65/17 Dueler H/Ts. Any difference may be a tire pressure issue also. I run the H/Ts at 37 psi, but found that the REVOs are better at 35 psi. Personnally, I prefer the control of a firmer tire over the comfort of a softer ride. I think it is mostly a matter of individual preferance.
If you try to order 16" wheels specifically, you might be in for a bit of a wait, especially this time of year. I think the factories are getting ready to change over to the '05 production, and special orders might be a problem. Another way to go is get the 17s and order a set of 16s separate. I found an outfit online that was selling the factory 16" steel wheels for $60. each. They were port pull-offs and in like new condition. Much less than the $160. ea the dealer quoted me.