I thought this might be helpful, I wrote it as a reply to another member's question. Please post your comments.
I have owned several 5 strings, I love them dearly and could not go back but the problem with them is their the setup. Violin makers don't have enough experience with them, but will never aknowledge this and talk like they know it all.
The extra weight of the extra string can be taken care of by using a raised sattle.
It is important that the spacing between strings is not the same, or rather, it can be the same as long as you don't mesure from the core of the string but from the edge. Violin makers have nightmares about this, but the 5th string is simply 6 mm wider than the 1st , and it vibrates much wider . You have enough spacing problems on a 5 string to be concerned about how well a violin maker sleeps.
Fingerboard planing is the other issue. Typically they will not have enough clearance for the 5th string to swing freely, while the middle strings are so high you can't hold a note for 5 seconds. If you are getting a new fingerboard, leave a lot of wood on the side of the G string (on my bass 15mm) while the B string side can have as little as 4 mm. Violin makers want a symetrical setup but the problem with this is that then the bridge is tilted towards the G string to allow for clearance on the B string.
It's my experience that thomastik spirocore and D'addario make good 5 strings.
