From: François Blais
Of course the scale lenght has a *big* impact on the tone.
If you use a 34" scale, you couldn't use regular upright strings with it. They're designed for 3/4 size bass scale (around 41") and you would loose too much tension if used with a 34" scale.
So in order to use bass guitar strings, you'll need to keep the bridge to tailpiece distance short. (and probably have to use extra-long scale BG strings)
I wouldn't use anything else than black-nylon tape-wounds BG strings to get a tone similar to an upright. (but I don't think they're available in extra-long scale)
So my advice is to go with a 41" scale.