You mean 4.5k and 9k. That's a difference of three orders of magnitude. The DCR, and output impedance of the pickup is not what you need to worry about, however, it's the input impedance of the preamp. MM pickups (Traditional ones wired in parallel, anyway.) have a relatively low output impedance. While I am not familiar with the MM preamp's specs off hand, it could be plausible that the input impedance of the preamp is a bit lower than most preamps, since the output impedance the preamp is designed to see at it's input is a little lower than with most pickups. If this is the case, the pickup might sound a little darker with the preamp than it would with other preamps, due to the more direct resistive loading against it. A lot of P bass players like this resistive loading though, so it depends on personal preference. It's a subtle difference anyways.
The impedance is probably a standard 1M Ohms-ish, though.
