Generally you pick a guitar and blow a saxophone...this would be a good starting point.
But seriously...I agree completely with Dave. What criteria did you use to choose these two from the dozens of excellent sopranos out there. If you loved your Mk VI, you might want to look for a good Buescher TruTone...exceptional for ensemble work and classical settings with great intonation and keywork not unlike the Mk VI (except those crazy palm keys). But any of the Yanagisawas would also be a great value with better intonation than the MK VI, but similar tonal quality and response. Don't know where you are, but if you're in a major metro area, find a couple of music stores and play some horns. The 475 is a pretty good horn overall, but generally costs a lot new (seems like you are looking at new horns) and loses value quickly. Once you narrow down what you want, you can consider some used horns here from reputable sellers that have overhauled them.
Examples that might be better than the new horns you list for less money:
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