I don't know how into podcasts you folks are, but if you look up NACOcast (put on by Chris Millard, principal Basoon of the NAC Orchestra) there's a great interview with Joel about fifths (though it's not done with bassists as the intended audience). He talks about his bass a bit on there.
http://www.nac-cna.ca/en/multimedia/podcasts/index.html: it's the 04.10.2006 NACOcast episode
Joel is playing regular 3/4 Dominants, so I'm guessing his string length is somewhere around 41-42" - anything longer than about 42.25" won't really work with those strings as far as I know.
As a side note, I've talked to my prospective new teacher and I will be starting studies though my university in the fall with him. He is a 4ths player though and through, but we talked a bit and he said if I want to try 5ths that he'd go with it. We agree on a few big tuning independent issues (use of extension fingerings/pivots, the amount of thought that should be given to Simandl, etc.) so I think it will go very well.
I'm hesitant still, but if I'm going to do it I should do so before I learn all the repertoire in fourths, and while I'm young and can learn quicker... we'll see!