The way I see it B string performance is more linked to construction (primarily neck stiffness IMO) than scale length and I think string choice and technique are more important that most people realize as well.
That said, all other things being equal, adding an inch in scale length will add tension and thus improve E and B string performance and clarity.
Sustain is a little better in a 35" , but the action is a little sloppy - if you play fast or funk or Jaco-like stuff you will need a 34" . If you play 80's rock ballads like Journey or Foreigner you'll love a 35".
the 35" strings will vibrate a little wider and if your bass is not set up properly, strings tend to buzz against the frets if you pull too hard, especially near the mid section of the bass around the 12th fret or sometimes the near the nut were the strings a just a few mm away from the frets. - in my experience, when you own a 35" you get a better fuller natural sound from the added length of string and more vibration. but it can be annoying playing hard and fast simultaneously. slapping takes extra precision on a 35" if you play fast.
34" is widely accepted as the best ballance between good action and a playable tight sound and enough string resonance. bigger than 35 and your strings turn to noodles. shorter than 34" and you loose sustain and warmth.
I realize this is an old thread but there is quite a bit of misinformation in this post.
The action of a bass has nothing to do with scale and everything to do with construction and setup. There's no reason the action on a 35" would be inherently "sloppy".
The vibrations of a 35 scale are SMALLER than that of a 34" scale given the same amount of attack because of the higher tension. The notion that the string "sags" in the middle under it's own weight like a clothesline is ridiculous. These are stainless strings, at high tension and the 35" scale adds exactly ONE inch to the speaking length.
Your strings certainly do not turn to noodles above 35" scale - quite the opposite. And you don't lose "warmth" with shorter than 34" scales, you gain it. All else being equal the strings are looser and that translates to big, bassy and warm notes that do lack the clarity and attack of longer scales.
It's quite easy to test any and all of these notions by simply (and CAREFULLY) tuning your bass down or up and seeing the effect on the strings and sound.
Have you ever noticed that the D and G string sounds weaker on a 35 scale bass? My new 35 scale gecko warmoth sounds really great on the H,E and A string, but the hightest strings just dosent have that meat. My other 34 basses have a much more "even" sound between the strings. And I have tried saddle- and pickup-adjustments
What you're likely experiencing is that the higher tension means less string vibration and thus not as much volume for a given amount of attack which is especially noticeable on the D and G. The D string particularly is often the highest tenstion string to begin with.
Increasing scale length obviously increases tension and can add clarity to the E and B strings but of course it also changes the timbre of the lighter strings as well. Whether or not you like that change is personal preference.
Some solutions to getting more even string response are to use a multiscale setup as Dingwall and others do or to use "balanced tension" string sets of which there are now a few different options.
Otherwise for a given scale and traditional strings it will always be a compromise.
