For reference, I tuned my 5 string NG-2 to G# standard (G#C#F#BEA). The Dingwall took the .142 with no cutting and handled G# like a monster.
A G# .142 pushes about 35 pounds of tension. If you take the same string and tune it up to B, you're going to go from 35 pounds to 50 pounds. (This is assuming your top string is a 37" scale length)

A .150 is 40lbs@G# and 56lbs@B
Your best bet is likely to go with a .136 which is 32lbs@G# and 46lbs@B
That 32 pounds might be sloppy, but I dunno. Kalium recommends a tension of around 40 pounds to keep it as close to a standard BEADG feel as possible, and usually ±5 pounds is acceptable. I believe when you buy ultra lights, you're going down about 5 pounds, and when you buy "heavy" gauged strings you're going up about 5 pounds.

Your mileage may vary, but check out the chart to see what options you might have.
http://store.kaliumstrings.com/TensionC ... _length=37

Thanks for that custom string gauge site/chart. It really makes things easy to figure out !