Ok, I just paid attention and clicked on your name 🙄
It’s a bit complicated now as you have a reasonable PR with Google (I know that’s not the most important thing with search but it an indicator of sorts). It can be painful with Smugmug (and also with Zenfolio according to don) to get Google to pick up your images quickly.
Most important is to know where your sales are coming from. If you are getting sales through Google search or even image search then you really care and maybe don’t want to move. If your traffic is direct then you don’t care, just move the site.
Smugmug probably may not be ideal if you just one ‘fire and forget’ for sales as it still only handles USD. If you want GBP you need to mess around a little and it sounds like you are trying to avoid that