Plinius SA250 Mk.4 vs. Pass Labs X350

Unfortunately, I live in the Sierra Nevada Mountains near Yosemite Park. The closest high end audio stores are three hours away and they don't carry either Plinius or Pass Labs. To go to the greater Los Angeles area to hear these units would be over 8 hours away and LA is always a nightmare to travel in. So I'm hoping so of the audiophiles here can be helpful in my making a decision.

I emailed support at Plinius to ask the very same question about the Mk. III vs. IV. I'll post the answer when I receive it.

Here the reply from Plinius support re: the difference between the SA250 Mk.III and IV.
The detailed changes in the SA250 are...

MKII And MKIII Started Approx April 1996 through April 1999
Serial number 7641 to 8931. Wired with the original Siltec cable. ALL MKIII wired with Generation 3 Siltec. U chassis design. Neither up-gradable to MKIV Single Transformer. Easily identified as not being a MKI by checking for 4 positions for ACS switch on the rear panel. Not easy to tell MKII and MKIII apart, only cables changed. MK IV Started June 1999 through today. Serial number 8931 onwards. Wired with Generation 3 Siltec. H chassis design. Quad Transformers. Easily identified as a MKIV by checking for 6 Countersunk screws on the rear panel or having a removable base. We believe that the MKIV was a step forward sonically. The power supply in particular seems to have added a degree of extra refinement and weight.