I know this will prolly never get looked at... But ah well.
There's a discrepancy between the PAL and NTSC A8's clock frequency, which is not unique to the A8 - it affects Commodore machines and other consoles too. This is because of the CPU clock being derived from the timings needed to make TV work (colourburst signals and such) so there's precedent for machines in different territories running at different speeds - most noticeable in music.
The clock pulse may also be affected by the input voltage - I'm thinking in particular of the Voltage-controlled oscillators I use in analogue synthesizers. Even digital watches lose time when the battery voltage dips, and handheld computers go whacky when the voltage is too low.
Try benchmarking both your units on a reliable DC adaptor. It could even be that one of your Lynxes shouldn't have mad it through QC and had a funky chip somewhere.
RE: Lynx II