Coming back late in this thread because i remember (is been long time since with VM) when had vm 100 mbps service was giving me 60-80 mbps in speed test about 2 meters away (with a pc tower)
I have a silly suggestion but i think will make difference
Next time when you have time, or anyone having this model to try ... can you swap the antennas?
Example ... swap the left with the right one or the middle with one of the ends