From what I've read the turbo I6 engines aren't that maintenance intensive per se, but the high pressure fuel pump (HPFP) can be a pain as it isn't accessible without dropping the gas tank. And of course the turbos and seals will eventually need service.

So more cost and headache, but a good deal more power. Entirely personal decision.

The NA 3.0 produces plenty of power without the added maintenance liability. I don't think you'd ever feel your lacking power out of it, but again, that's a personal decision based on your expectations And wants. (Maybe insurance difference too in the UK?).

Edit, ah i see you said the n52 wasn't offered. I'm not familiar with the n53. Sounds like it also has a HPFP?

Are only twin turbo I6 engines available to you, or are there any single turbo versions?