Many people (e.g. Eric S Raymond) would argue that this type of efficiency gain from switching to a communist economic model is only experienced in the software industry. The reasoning behind that would be that software (and other digital ~~content~~works) has special traits: it is cheap to produce and infinitely reproducible (the economics of free software are essentially post-scarcity economics).
On the other hand, certain industries, like the mass production of clothing and mining for precious metals, would massively lose out as a result of a communist economic model because they can no longer extract maximum value from laborers by underpaying them and must provide quality working conditions, which would result in a decrease in productivity. Additionally, there would be an allocational problem: if a resource is scarce, where should it be sent, and for what purpose should it be used?
It should be noted that I'm not intending to criticize socialism in any way - it's just that socialists should gain a better understanding of economics so that socialism can be presented as a highly sophisticated alternative economic system rather than some knee-jerk ramblings.
EDIT: Crossposted your post to /c/debatepolitics in a shameless effort to promote my community :)