one problem is that it's impossible to measure the speed of technological change. "Technological change" involves a bunch of heterogeneous alterations in the ways that things are produced and in the list of products that are possible to make. As such, as a sum of apples and oranges and purple logarithms, tech change can't be added up. So we can't measure its change.
The most common way to measure tech. change is to measure its impact, say, by looking at labor productivity. But "labor productivity" is also an aggregate. I'll leave the denominator (the total amount of labor-power hired or the total amount of labor done during a specific time period such as a year) for some other day. The numerator is a sum of all of the commodities produced during the specific time period (year). The different commodities are added up by first multiplying each of the commodities by its price. In the simplest case, you use the price of the commodity in a specific year (the base year). Keeping the price constant avoids measuring inflation along with labor productivity.
The problem is that the prices reflect the priorities of society. That is, under capitalism, the prices (not to mention the output) reflects the profit-seeking nature of the system. There are lots of important goods, such as free time and the natural environment, which lack prices.
Now, if you're interested in measuring labor productivity _under capitalism_ that isn't a horrible problem (though we should remain skeptical and always examine statistics carefully). But comparing productivity and its growth between capitalism and any kind of socialism is very very difficult. Socialists might decide to put a price on the natural environment (in some unknown way) while setting the price of important subsistence goods such as milk at zero. This would distort any comparison. Labor productivity might grow more slowly with socialism than under capitalism because so many products would be assigned low or zero prices. Or maybe hypothetical "shadow prices" (which no-one actually pays) could be used. But even these would reflect the priorities of the society.
Strictly speaking, labor productivity can only be measured over time by looking at how the same product is produced in different eras. But some products _can't_ be produced anymore, such as the stained-glass windows windows in Medieval cathedrals.
A long time ago (the 1970s), economists Fogel and Engerman argued that the labor productivity of the slaves in the US South was high relative to that of the free workers in the North. But this turned out to be because the price of cotton -- the main Southern product -- was temporarily high. Also, labor productivity is raised by rising intensity of labor (as under whips).
Jim D.