My first "real" camera bag was a Crumpler 5 Million Dollar Home. It was fine for my 2-lens DSLR setup but nothing else. That was when I learnt that the bag must be able to contain other essential travel items as well. So I sold it and bought a Billingham Hadley Pro which gave me a little more space to work with. (Interesting fact: it was Kai of DigitalRevTV that got me interested). Later on I kept the Hadley Pro when I downsized to m4/3 and found that it was just right for traveling with a m4/3 system. You'll be surprised how little things add up when you are in a foreign land.
I basically divide the internal space into 3 compartments, with two smaller side ones and a larger center one:
1. Left compartment: 1L water bottle (just nice and very useful)
2. Center compartment: E-M5 body, 12-50mm lens, 25mm f/1.4 lens with hood (doesn't matter which lens is mounted, they can easily fit)
3. Right compartment: camera accessories and valuables (plenty of space for wallet, passport, phone, etc)
4. External pockets: maps, tickets, tissue paper and other misc items
The loaded bag is comfortable to wear all day. It also fits under the seat in front of you when on an aircraft, so you won't need to put it in the overhead compartment if you don't want to (i.e. if your passport and other valuables are inside). Best of all, it is weather proof so you never have to worry about your gear getting wet before yourself. (Tip: keep a disposable poncho inside the bag!)
By the way the TS said he is going on a business trip. The Hadley Pro looks great with smart casual wear and has space to contain A4-sized documents or an iPad. Definitely worth the $300+ IMHO.