I'm certainly not a Conklin expert and I'm even less of a Roscoe expert. I have owned 5 different GT7's over the past few years (still have one of them) .... I've never owned a Roscoe or a custom Conklin, but I have played several of each.
With that said, I agree totally with John, you're comparing a custom built bass with a production bass. While I also agree with you (it has to feel/fit right), your comparisons would be much better suited to a custom Conklin vs a Roscoe.
I had the pleasure of visiting the Roscoe shop last summer (2005) and I was dazzled by what I saw ... it was a great experience. The craftsmanship is of the highest level and the basses are worth every penny. But for me, the bodies are on the smaller side and that doesn't work (for me).
I'm a big guy, and I need a lot of bass size for the axe to be comfortable. As beautiful as the Roscoes are, they are just too small for me. Based on my limited Conklin experience (production GT7's only) I can tell that the Conklin body style is far better suited to my needs.
In my case, I ended up ordering a custom 7 string bass built to my specs by another builder that I have a great relationship with. My advice, as with so many threads here, is to try the basses if at all possible. But, if you know that the Conklin is your size preference, it's unlikely that the Roscoe will work for you ... it's quite a bit smaller.
But dang, those Roscoe basses are just amazing .....
edit: Forgot to answer one of your questions ..... every Roscoe I've ever played was perfectly balanced, no neck dive at all. If it wasn't for the smallish (by my standards) body, I'd be playing one right now ....