Welcome! WDC licenses models for companies to build 6502 from, and I imagine it's one of those licensed builds which is touted as going so fast.
FPGA 6502 running at 50MHz isn't bad - it's certainly possible to do better, and of course it depends on how new and how expensive the FPGA is. And well done, a more cycle-efficient core will get an advantage.
The fastest 6502 these days, I'm fairly sure, is an emulated 6502. This is because of the great pressure on performance of general purpose CPUs, and the great price advantage of volume. A $10 Raspberry Pi can emulate a 6502 at around 300MHz, and a Pi 4 goes even faster. The PiTubeDirect project allows a Pi to be connected to (or in) an Acorn BBC Micro, where the Pi can act as a second processor, in a historically authentic way. It looks, feels, and acts like retro computing with a 6502, even though there's an embedded emulation involved (as well as a genuine 6502 and much TTL).
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