800V charging would be a complete waste of money, the Supercharger network is 400V and it will be years before a significant portion is 800V. The missing upgrade isn't 800V charging it's that the battery chemistry hasn't changed. Teslas have a lousy charging curve, they taper off too soon. The peak rate of 250KW is as fast as you ever need in a car. If you could maintain a flat 250KW rate you could do a 20-80 charge in 12 minutes. That's as fast as it ever needs to be because you can't go to the bathroom in less time then that time.

Doubling the voltage has zero effect on the efficiency of the motors. When you halve the current in a motor you have to double the length of the windings so it's the same amount of I*I*R losses but it takes twice as long to do the windings when you build the motor. You also need more expensive power transistors. You would also need to support split pack charging or include a power booster to charge effectively on Supercharger network. Both the Cybertruck and the GM trucks support split pack charging which is doable because those packs are much bigger than the packs in cars, in GMs case much much bigger. The Hyundai's use a voltage booster and their charging sucks on Superchargers, only 130KW vs 230KW on an 800V charger.

When they do the next refresh it might make sense to go to 800V because by then there will be a lot of V4s but as of today there are zero V4s. There are some V3.5s which can do 325KW at 500V which will allow Cybertruck and Silverados to charge at their max rate.

Chinese specs are 30% greater than USA. The reason for the greater mileage spec.

I can't find any reference that says the model y ever had over 400 miles of range. The website even claims it maxed out at 337 miles, not 427. Could the writers offer their source for this?

Model Y Performance Version ? Specs ??
Is Dual motor  ... 380 HP ? And
Performance Version 445 HP ?

Yes, but the problem is that all Chinese competitors at that price point have 800V-900V powertrains that offer 10-15 minute charging times, and some even offer drive-by-wire and rear wheel steering, not to mention the other extras and interior appointments. The Juniper will only fly in the US and Europe with those aging specs.

Middling specs? It's a car aimed at the mass market. Not a high end vehicle...