Is it more fatal to be trapped in a room with 10% more carbon dioxide than 1% carbon monoxide?

Carbon dioxide is effectively 0% anyway so either way it's 10%.

It would be considerably worse to be trapped in the room with 1% carbon monoxide (assuming the rooms exchange waste gases and the total concentration of gas does not vary over time). Whether it would be fatal depends on time of exposure but the CO room is worse than the CO2 room. That's because CO binds to hemoglobin and takes the place of oxygen (it binds about 200 times more readily than oxygen). So there is a cumulative effect to breathing CO. The room with CO2 would be similar to breathing at high altitude. 10% is the functional equivalent to breathing at about 5,000 feet -- roughly the altitude of Denver. In fact, one of the methods for testing altitude tolerance in the lab is to use a mixture of CO2 and air. Accumulation of CO2 will make you breathe faster to maintain homeostasis, but it is not fatal. So long as there is enough oxygen, you can breathe in a high CO2 environment indefinitely. That is not true of CO.