This may be changing the subject a bit but IMO i wouldn't get a rockbass. Pretty much every unique characteristic of a warwick is missing from a rockbass, and aside from the shape you will leave still likely wanting an actual warwick still if its one of your dream instruments to own. To upfront answer one of your other questions, unless the RBass necks are different than the German, pretty much every WW neck ive played is a "U" or "D" style shape thats wide with deep shoulders and a flat back... that said, even though i usually prefer thin C shape jazz necks, the Warwick U necks i find very comfortable.
The Rockbasses are missing:
1) Bell brass frets
2) Exotic woods
3) Open grain Ovankol or Wenge neck (im aware some Streamers use 5 Peice maple)
4) The MEC preamp (the RB MEC eletronics and pots are completely different)
Its been a while since ive tried one in person since no where in my city carries Warwick anymore for a while now, but when they were around it felt very 2000's squier (not todays quality of squier) caliber of an instrument for a significantly bigger price tag. I would save up a bit more and just get a used (or new) Made in Germany Warwick, especially because some of the older warwicks are the nicer ones IMO when they had Wenge necks... in fact i would almost implore you to get an older one because from what i see on their site now, the "Pro" or entry level MiG line is a cost cut version of what they were a decade ago.
To each their own... but if i had to pick between the JJ and $$ regardless of MiG or RB, id personally say go with the $$ or PJ Streamer. As i stated the preamps are different as far as im aware between the German and RBass instruments, but I had a german Corvette with Jazz pickup configuration with specs similar to the Corvette STD but with maple body. I predominantly play Jazz bass pickup configuration and nothing i could do with that bass could get it to sit in a mix nicely. It sounded "growly" or kinda alright on its own albiet a bit thin and overly agressive and midrangey... but as soon as i was in a band setting (one metal, the other Rock) i either dissapeared without great lowend, or my brittle sounding mids and highs would cut (in not a good way). I ended up selling it a few years back, but since have gotten a Thumb NT where i prefer the pre and pickups in it. Just based off that, i figure you are likely to have better luck with the $$ or PJ.
If you have the option to rent for a week, i would likely suggest renting one to make sure you don't go through the same thing I did where the German corvette felt great playabilty wise in hand, but had a sound i couldn't work with that just got worse when i put it in a band or recording setting. Obviosuly its not always a possibility to try and compare everything unfortunately, let alone in a band environment before purchasing.
Ive owned a WW Thumb BO5, CorvetteST, and the late 90's thumb NT, if you have any other questions based off my wall of text let me know!
