Synthmeister,
Have you looked at any of the KETRON (formally Solton) products? Based upon your needs and requirements, this would surely be one of those you would want to 'ckeck out' prior to making up your mind. Take a look at the KETRON X1 & the KETRON SD1 keyboards. I won't say much about them because you NEED to check them out for yourselves ... I will say this though - they both have sequencers (150,000 notes) with the X1 expandable to 300,000 (if you add extra SIMMS chip)!
Bon voyage!
AJ