Hi,
I would definitelly recommend the PSR 740. It has (almost) the same instruments as the PSR 8000, good styles and nice price. I tested the MZ 2000 shortly, because after short time playing it I was very disappointed with the sounds and styles and went home. The MZ 2000 could have better features than the PSR 740, but the quality instruments is much more better on the PSR 740.
That is my recommendation, you should go to the music shop and compare both keyboards - you will hear the difference.
Regards
Marek