I just installed the Big Splits in a "Mule" bass of mine (routed out for any pickup combination you can dream up).
Just playing through my little practice amp vs. a Mexican Jazz bass setup I can say there is MORE of everything. Like 15% more sound, it's like the difference between slightly overcooked fish vs. fish that has been cooked just long enough.
Maybe that's a bad analogy.
Anyway, my only complaint is they are really bright and zingy/modern even with the tone knob zeroed out, so if you want old school, I think these are the wrong pickups. They are Hi-Fi. They have a very nice grind to them. If you want to punch out of the mix these pickups are nice. They remind me of a jazz bass with an active preamp - except you don't need the preamp to get the sound.
I've read that the big singles are even more zingy (highs, high mids), personally I don't think I'd dig it, this is about as much zing as I would like to hear out of a bass. I am more into low mids and mids.
I've got a Fender preamp I'll install shortly and see what happens then... first I need to take this to the studio and try it through the SVT/Berg rig. The Fender Rumble 25 is not exactly the warmest sounding piece of kit.