test drove the 523 followed by the 528i today. on paper, the 528i is much higher specs (bhp & torque) than the 523. and during the test drive, the 528i indeed did feel faster than the 523, but i didn't think it was very much faster as i would have expected given the vast difference in the bhp and torque. no significant turbo lag when i pulled the 528 from stationary and the acceleration felt relatively linear. if you are looking for those kind of feeling commonly found in a japanese TC car (read: STi and Evos), then you will probably be disappointed. i also feel that while the N20 feels very 'raring to go', the N52 was more refined. the cabin noise (from the engine and exhaust) was noticeably louder (but not necessary nicer) in the 528i than the 523.
in terms of features, the 528i is better equipped than the 523 highline. the more noteworthy addition is the automatic start/stop function, park assistant, soft close and electric rear blinds.
it is a tough decision to choose between the 2. but if you take into consideration the discount that PML is giving for the outgoing 523, and thus the price difference between the 523 and 528, the decision becomes very easy. of cos, if $$$ is not an issue, the 535 or ///M is the way to go still.
just sharing my personal opinion. cheerioooos.