I know it is likely out of bounds for this conversation. (ie, new bike) But, a DaVinci drivetrain has the ability to have a larger gear inch range. The intermediate shaft is usually geared 2:1 from the crank (though that can be modified) so your front cogs run 2x the speed and are smaller. (ie 13-20-29 on the cogs is the standard crank/chainring equivalent of 26/40/58) While there are some gearing tricks inherent in that setup, the range bonus becomes more apparent when talking about chain wrap. With the front cogs being half the size you use up less chain wrap allowing for a larger rear range. For example, a 24-50 standard crank is a 26 tooth chain wrap leaving you with only 21 teeth in the rear (ie 11-32) for the 'legal' 47 tooth chain wrap. But if you are running a 2:1 on the DaVinci the 24-50 becomes actual gears of 12-25, dropping your teeth differential to 13, allowing you 34 teeth in the rear. So you could have a 11-45 cog set.
Again, this is more hypothetical and really only talks to the gear inch RANGE that can be achieved. If you are stuck with a standard Tandem drivetrain then I would just take some teeth off the top end and move them to the low end if you need the low gear inches.
simon