I would really recommend staying with the Pentosin. It just seems to work the best in the BMWs with ZFs. Just like with Hondas, I use Honda fluid in the Hondas and Pentosin in BMWs and never a problem. That transmission is actually pretty strong, and without crazy turbocharged power to it, it should last awhile. Most of those cars have 100K+ miles with the original fluid.
My friend's e90 (325xi) has the GM trans in it with original fluid at 114K miles. It shifts fine, but I do have the fluid to do the change, just haven't gotten to it yet. The ZF trans is superior in my opinion. I met a guy with an e90 330i with 270k original miles. He just did oil changes every 6k miles and fluid drain and fills every 50k in the ZF auto. I've used MaxLife in other vehicles with good results, but considering how expensive transmission work is on a BMW, I think sticking with the OE fluid is ideal.