To try to speak to those points...
Moving to a 45 profile tire *will* improve
the overall responsiveness. A shorter and
stiffer sidewall will provide this, and the
effect will be even further enhanced by good
tire selection (for example, a desigh with a
solid center rib).
Moving to 215/45/17 on a non-lowered car (I
am assuming you are using an approved wheel)
should NOT rub. Tire Rack will guarantee the
fitment if you buy this size from them with a
reasonable wheel choice. I have heard that a
few people rub with this size at the 38-40 mm
offset mark when lowered, but that is it...
You *will* incur some ride quality loss, but
a good tire can help offset this. It will not
be a jaw-shattering ride simply by going from
a 16" wheel to a 17" wheel. If worried, pick
a tire like the Dunlop SP Sport 9000 which is
very highly rated for maintaining a good ride
quality in lower profile sizes.
T.
