Looking at the data, I'm inclined to agree that not much CPU is saved, but the point of MessagePack is to save bandwidth, and it seems to be doing a good job at that.
Significante with regards to what? Not doing anything? Flipping the toggle to compress the response?
To me it doesn't. There's compression for much bigger gains. Or just, you know, just send less data?
I've worked at a place where our backend regularly sent humongous jsons to all the connected clients. We were all pretty sure this could be reduced by 95%. But, who would try to do that? There wasn't a business case. If someone tried succeeded, no one would notice. If someone tried and broke something, it'd look bad. So, status quo...
I've tried messagepack a few times, but to be honest the hassle of the debugging was never really worth it
Thus, the only thing you can do after that to improve performance is to reduce bytes on the wire.
In a discussion about using messagepack that doesn't really sound like messagepack is winning.
99.9999999% of the data sent across the network in that Datacenter will never be read by humans directly. Why put it into a textual form?