Before buying...you should drive the I6 and the V8 to see if one appeals to you or not...regardless if you are leasing or buying. Everyone's driving style is different...the I6 may provide you with enough power/performance to be satisfied...whereas to some...it may feel underpowered and the V8 is the only option for them.
You have to determine for yourself which engine works for you. And the V8's oil issues tend to be associated with the early renditions of the N63 (the N63TUB44O0)...BMW is now up to multiple engine upgrades since the debacle that caused them to recall those early engines.