The M112 is a better size for the 4.0 litre engine, given the capability of our engine to rev.
To produce useful bost out of a M90 you need to rev it fairly fast when the engine isn't revving fast. When the engine gets to 6,000rpm the 90 is being over-revved.
The 90 may give a bit more torque down low (if set up for it) but the 112 will give a wider (usable) power band.
The 90 can't service both ends of the powerband like the 112