The feeling of boost will trump the screaming V10. BMW NA engines were tuned very well and don't leave a lot of power on the table. I suggest just doing a custom turbo on your current engine. When preparing your drivetrain for more power, it is not the HP you have to worry about...but the torque. Being that the e70 chassis can tow, it should be able to handle a lot of torque...which means you can up the boost.
Just remember the tune is the most important thing.
Generally BMW swaps are very expensive and it can be hard to find information. I also suggest LS vs a BMW swap. You can find tons of info on swapping an LS. Also there are companies making LS swapping parts for BMW chassis.....engine, transmission mounts, exhaust, etc...
Engine swaps are not for the weak.....but like most situations money is very powerful and can make things happen fast.
You can find some good info here to get more familiar with engine swapping in a BMW.
https://www.bimmerforums.com/forum/s...ing-Start-Here!