Just make you sure you don't buy a blower style Vega ( single fan cooler) for ANY reason.
A lot of the really low priced ones are that style, and thermal issues mean they leave a fair chunk of performance untapped.
I have a Vega 64 liquid cooled card. They have the most aggressive bios, and kind of need liquid cooling lol.
Strix Vega 54 air cooled , for example, come pretty close to LC specs.
The reason this matters is, more aggressive bios = higher clocks at stock = more heat and power.
So if the 64 that is only 50 pounds more has a decent cooler on it, and the 56 you are looking at also has a decent cooler, then the price difference would arguably be "worth it"
However every tech youtuber out there will tell you to buy a well cooled 56, overclock and undervolt it, and get very nearly 64 performance.
I can see why you ask the question .
At 399 pounds a decently cooled 64 would be a pretty good buy I would say.
However....... CES is in a couple week. Rumours are flying about new cards being announced, at 56/64 levels of performance, for a lot less money.
Going to say don't buy anything right now, if you can help it. By the end of January or so we should have a lot better idea of what is coming, at what price, and when.
Because if you could get a 64 performance, plus 15% ( which is the "leak" info), at under $300 USD, by, say.. March?
You would kick yourself for spending more money for less performance.
And yes, 56 and 64's are good at "stock" , now that the prices are decent.