Sir,
Please know that I am NOT a current pilot and even when current I never flew the Big Machines for which V1 and V2 are such apparently critical numbers. That said, I do understand the physics behind these calculations. The basic formulas do include a modest fudge factor, always in your favor. Despite that fudge factor, and understanding the rather simple math, I'd 'fudge' V1 a bit lower and V2 a half-a-bit higher. Of course the Flight Operations Departments have other ideas and pilots may be called to task for even minor variations of their calculations. Your question is about safety, so 'error' on the safe side and give yourself that extra second of wiggle room when (if) it goes to hell at the last instant. If the performance limits are already being stretched (Hi and hot with old engines) hike up your already too tight shorts and delay your departure, dump some cargo or pax or whatever will improve your numbers enough to make you comfortable. In other words, please don't fly the margins as far too many do. Have the [anatomical parts] to say NO when you don't like the numbers. How do you know that both of those engines will perform at 100% or 105% when you most need it? (I'd suggest that most will not - and it is not worth your life and that of your 100 - 500 pax to find out. If you're not 110% comfortable, please do not fly or wait until conditions improve. And it really is that important. Ten percent can make the difference, fudge factor or not. -C.