Although I've never played a Sei, I've gotta go with Jerzy Drozd here. His basses are perfectly suited to me. It's almost like his basses were designed with my preferences in mind! Fantastic neck, very versatile tone-wise, and ergonomically superior to anything I've played. The body is very small, with most of the mass of the bass being in the neck, but because of the extended upper horn, his ~9 pound basses feel like they weigh 7! My Drozd has his split-coil pickups, which when blended equally sound very fat and warm, but with lots of growl. The neck is assymetrical; it's chunkier at the top to be more comfortable on the thumb, but thinner on the bottom for fast playing. It's also very flat, which is comfortable. The fingerboard radius is 20", which works very well for 5 strings, and makes string height adjustments at the bridge a breeze. The bridge is another nice feature of the bass. It combines beauty with functionality.
If you can take the 10-12 month wait, they're well worth it.