Yes.
Yes.
Speaking as someone who used to coach at altitude (higher than Utah), these athletes definitely run faster when they get down to sea level to compete (even if they grew up at altitude). But, in the case of 4,500’, the standard calculators are too generous. It’s worth about a second per lap from that elevation, so 3:58 and 8:28 +/-. Anything lower than 3,000’ & there’s no point in doing a conversion. It gets parabolic the higher you go.