Considering an e61
 

I've had many BMWs, but nothing new than the e46 330xi 5 speed I have had for the last 7 years/140k.
Its time to replace it and I could really use a wagon or SUV.
I drive a lot these days (4-500 miles a week)
I live in snow country, so AWD is a must.

So...
I'm thinking of an e61 and if someone can point me to some good general threads I would appreciate it, but one big question is 530xi vs 535xi.
These days I am less concerned about power and speed than reliability and mpg.
I assume that points to the 530, but I'm wondering how much difference there is in practice terms for both maintenance cost and mileage.
I do the majority of work myself, so another factor is whether the twin turbos engines are a lot harder to work on...

Thanks in advance.

N54 (535) takes a lot of money to be reliable but once it has fresh parts (turbos, injectors, walnut blasting, plugs, coils) it is quite a nice/strong motor. If you want reliable, I would look at a well cared for earlier model.