The M52 B25 lacks the rich torque curve the B28 has. Ironically the M50B25 has similar power to the M52B28 but again its in a torque hole, that being said if they are buzzing past 4k rpm there is little to differentiate them As to the M54b30 vs the M52B28, having owned both I am unsure why the B28 would be more highly regarded, both rev cleanly to redline and the B30 has very nice torque delivery. putting an M54 crank rods and pistons into a B25/28 is a popular swap.