Hey bro,
Since you are comparing an 50k with 160k. This is what I will do if I were you.
I will go check out F10 as well, compare it with E60. If you prefer E60 than F10, then for sure you should buy E60.
But i guess most probably you will prefer F10. Then why not buy E39 now and save the 100k first, 5 years later when F10 price dropped, then only buy F10.
In fact if you are comparing E39 with E60, and their price is 100k difference, that means E39 should be the wise choice. And you can still upgrade to F10 5 years later. Why not?
But if you prefer E60 than F10, then of course go for E60 now lor.
Make sense?
If you have not own a bimmer before, it's also better to get a cheaper entry to experience it first. I have also bought my first bimmer few months ago E39, a strange thing happened to me. After I own a bimmer, I started looking at Audi. Haha!