For those rates, I'd definitely book the Lincoln. That will give you maximum flexibility at the Hertz location if you end up seeing something else you like. A confirmed luxury car rental commands more attention than a confirmed SUV or premium car.

This completely goes without saying but I'll say it anyway: make absolutely sure you join #1 Club Gold before the rental. Drop by your local Edinburgh location (I'm sure they have one or more) if you need to sign anything. I don't know how this works internationally but trust me: your life will be much easier if this is taken care of ahead of time. (My apologies if this is basic "Yeah I already knew that" information. )

For people who for one reason or another can't get their #1 Club Gold set up before the rental, I usually recommend Priceline. If ya gotta stand in line, you might as well get the cheapest rate! If a premium car really would suit your needs, I would do that: a bid of US$25-30/day would do it, about 100 GBP for the week. Bidding luxury/SUV on Priceline is squirrelly - sometimes great deals are there, sometimes they aren't. Your GBP182 rate for a lux car is pretty good - I'm not sure if PCLN would beat it or not.