You should never need more than the equivalent volume of a 26" roller bag and a 20" roller bag for a trip. Personally I choose the following config: 25" rolling duffel (around 8 lbs) and a convertible backpack (about 3 lbs but holds as much as a 22" roller). I go about a month with this.
I check the 25" and carry the convertible. You should definitely be able to put suits/business clothes into the 25".