I dont see how the distortion specs will differ. Im not arguing I just dont see how or why the sound quality would differ between the amps. The missing caps would affect the POWER if anything, not the quality of sound. ALL US AMPS of that era were built AMAZING. The parts inside are of the highest quality. I dont see any difference between any of the lines. I would love for you to put the VLX head to head with a VL 400 and a USA-400. The only difference on the VL is that you get to adjust the sound slightly. Sonically it should be the same.
EDIT:
Actually after thinking about it, I would expect the distortion specs to double on the VLX since there is double the circuitry.