They change rapidly. So in that sense it's not stable at all. No benchmarks at the moment. I haven't noticed any lag at all. I would imagine that if you have enough memory to keep all objects in memory, it will be as fast as you could possibly want on a modern desktop machine.
Most time is spent waiting for input and packets.
And python can hypothetically be compiled into pure Java. And Java can hypothetically be compiled into native machine code. So basically yes unless you optimize, but speed isn't the only important thing. Nor security audited. Well, I suppose you could count me.