I think I may have been the source for that 170V measurement, and it's incorrect, it is probably the full 300V advertised, or close to it. I recall at the time I couldn't figure out a place to measure plate voltage without major disassembly, so I could only get to the tube pins easily, that was 170V so the supply must be higher. How high, I don't know, but I recall the cap near the pin, which I'd guess was part of a voltage multiplier, was rated at 250V (or was it 350V??). That fact, plus ART's strange marketing statement, probably confused me into accepting my initial incorrect measurement.
That was a year ago, since then I have used the pre nearly exclusively, and it's a screaming buy at its price. I love practically every feature it has. Quiet, good converters, the impedance feature is very handy, lots of tonal options between that and the ability to set level going into the tube. I almost never use the low plate setting though, the high plate voltage sounds too good.
The only minus I can think of is the pots on mine are scratchy. I haven't bothered with lubrication, it hasn't troubled me that much.