Next step up in steth for student

I own several steths, and overall I think I like my Littmann Classic II SE the most (out of several Spragues, though they are nice as well). I was wondering two things of the community here:

1) As much as I like my Classic II SE, I was thinking of upgrading to the Master Classic II due to simplicity in the scope head design and improved acoustics. DO you think I would really hear the differences between the current classic II SE and the Master Classic?

2) On the other end of the spectrum, I'm looking for a less expensive stethoscope to take to clinicals in 'dicier' parts of town, or for use in busy hospitals where they may walk off. I really like the Sprague style stethoscopes. Presitge makes a Clinical Sprague with a 16" tube, and they make the standards (with ~22-24" tubes). Anybody think the shorter one would sound better? It's more expensive, but if the acoustics are good, I'd be happy.

Should I, as a student who is prone to losing things, go up in value to get better at auscultations, or should I stick with lower to mid-end steths, and if so, which ones? (I do like the Sprague style, so advice with those is appreciated).

Thanks!