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Ah, it's been long since I compared a 3750 vs. 3850, I now think the resource improvement, or lack there of, I was concerned about was TCAM (as we're implementing IPv6). However, after my confusing buffer RAM with TCAM, please don't hold me to an accurate comparison between those two either, as I got the buffer RAM difference so wrong. (I.e. I believe 12 MB of buffers for 48 ports is better than a 3750's 2 MB per 24 copper ports.)
Regarding the other performance differences between the original 3750 series and the 3850, you're spot on, and they can become issues, but my experience with 3750 series, you're more likely to see output drops (as you mention in your OP) and those are often caused by the 3750's limited buffer RAM and the way, by default, it manages that buffer RAM. (When I noted I've had some success with 3750 buffer tuning, for a SAN device, I went from multiple drops a second to a couple per day.)
In your OP, you were concerned about avoiding the interface drops you're seeing on the existing 3750 and in you follow-up post, you're now hoping to use QoS to optimize performance.
Well, to the latter, you can do some very interesting things with QoS, and some of those things do include improving performance. However, cannot comment whether your proposed QoS implementation will hurt or hinder, as I don't know what you're trying to accomplish nor what your traffic is really like.
I will say, as your OP principally expressed concern about minimizing your drops, although most everyone likes zero to few drops, drop management is an important, but often overlooked part of a QoS. I suspect you realize this, as you new post has WTD in two classes, but, again, whether what you've defined, will help or hinder, I cannot say.
