Jim & Bubba have it right.

In your examples, the 11-6 will have greater efficiency, simply through having greater diameter, but it also has a slightly greater engine load than the 10-7. The engine will rev somewhat higher with the 10-7 & the model's speed will increase -- from the effects of both the rev increase & the steeper pitch. However, assuming the engine's revs don't fall below its usefull power band, the 11-6 will quite probably produce greater thrust due to the larger disc area & better overall efficiency.

For 2-stroke engines in the 40-75 size range, and assuming 2-blade props from the same manufacturer, made of the same material, & of the same style -- the rule-of-thumb for power load matching is: increase diameter 1", reduce the pitch 2". Conversely, reduce diameter 1" & increase the pitch 2" (1" of diameter is more-or-less equivalent to 2" of pitch in terms of engine load). This relationship obviously results from the fact that power load increase more rapidly with diameter, than it does with pitch.

Using the rule-of-thumb and taking your 10-7 as the baseline prop, an 11-5 would be a closer power load equivalent than the 11-6. The 11-5 would definately produce more thrust than the 10-7 (greater diameter & efficiency, same power transmitted). The model would accelerate & climb faster, but it would also decelerate faster & be slower in level flight.

Prop matching is a black art that comprises both theory & experimentation. The final "best-fit" is highly dependent upon the engine characteristics, the airframe configuration, the prop manufacturer, material & style, plus the intended outcome in the particular application. The theory will get you close & cut & try experimentation will finish the job. It helps to have lots of props in lots of sizes.