Advertisement for the Monroe PC-1421 Desktop Printing Electromechanical Calculator
It is interesting that this advertisement claims that the PC-1421 is "as fast as any electronic calculator" except it's own electronic calculator, the EPIC 2000.
This claim is certainly cast into doubt when the PC-1421 is compared to display-type (those with numeric indicator displays as opposed to some kind of printing mechanism) electronic calculators, which were undisputably faster than the motorized mechanical PC-1421 calculator. However, the ad is careful to claim that it "gives printed answers as fast...", which qualifies the statement to indicate that it's faster than any other printing electronic calculator (other than the EPIC 2000).
The only other printing electronic calculator on the market at the time the EPIC 2000 was introduced (December, 1964) was the Mathatronics Mathatron, which, by design, allowed math problems to be entered just as they would be written on paper, providing the overall answer to a problem when the [=] key was pressed. The EPIC-2000, along with the electromechanical PC-1421 calculator required a problem to be broken down into steps that suited the calculator's arithmetic system, thus requiring more time to enter the problem into the machine, as well as possible need to write down or store intermediate results for later use in the calculation.
Bottom line, it's pretty unlikely that the PC-1421, with its (amazingly complex) mechanical wizardry, would be able to out-pace the Mathatron in anything but perhaps the simplest of calculations, where that Mathatron's serial (digit at a time) printer would be a handicap compared to the PC-1421's line-at-a-time printer.