If this is your first Tesla, or first EV for that matter, I always give this advice. You're not buying a car, but rather a piece of technology, like a PC or a cell phone. Buy the newest one you can afford and forget about buyers remorse since there will always be a better one. In some cases, the very next day you buy yours, a better one comes along.
That said, specific to your question, how important is the acceleration to you? Is it just for bragging rights? The new MS has a 3.1 0-60 time vs last year's MS Performance at 2.3. Just a reminder, 3.1 is plenty fast and can out accelerate about 95% of all the cars in your daily commute. The range is very significant, 412 vs 348. That's over 60 miles, and can make a difference in everyday living with an EV.
Don't forget about all the new tech in the interior vs circa 2012 interior of the 2020 Performance you're looking at.
If it was me, I'd go with the newer one.