I've heard about the 80% trick with passive basses, like P basses and J basses, and I attribute that to the "optimal load" that the pickup wants to see, relative to the resistance setting of the passive volume and tone controls. However, with an active preamp in place, you shouldn't have this problem "at all". Unless you're overdriving your preamp, in which case this will be the least of your problems.
The short answer is: it depends on your preamp. The same effect of pickup-relative-to-controls, can be obtained with bass-relative-to-preamp. In other words, if you're using a solid state pre with a low impedance input, you can probably expect to get a little boominess (in that situation, many people use a compressor to address this). If you're using a tube pre, or your solid state pre has a high impedance input, there should be smoother dynamics. A low impedance signal source should mitigate both situations, so my recommendation would be to go active, and only revert to passive mode if absolutely necessary. At least that would be a good place to start.
