Warwick Thumb NT 5 string without a doubt, ACG Krell is very close, with MM SR5 as a very decent runner up. The Thumb is definitely "thunderous" but you'll need backline/PA support capable of accurately reproducing that low fundamental. I had a Barefaced Big Twin T that was absolutely brilliant.
All of these are 34" scale and I tend to use 130 B strings, I've played 125 too, doesn't seems to make much difference.
Alan Cringean quite rightly identifies rigidity of construction as being vital for sustain and clarity, which jibes with what many people are saying about build quality and construction.
That said, I played a 5 string Steinberger which didn't sound great, but had huge rigidity.
I'd go play some good 2nd handers, you can't afford to get into Fodera, Alembic etc territory, but there are plenty of very good old basses around for £2500 ish, my thumb was about that I think. In theory, any decent luthier's work should produce a B string of quality, but there's more to a great 5 string than a big B.