RAT 5: indeed, things have changed. I did start out with the Binder of performance charts and only using ATM as method since otherwise it would have been too much work to get the right figures. One knew roughly which figures would be the result from which conditions, and as we flew a very limited network, for which runway.
With the switch to the EFB and the combination of ATM and derate that "knowledge" became obsolete, as very very tiny changes could lead to wildly different performance figures. In effect we had three differently powered aircraft in one, flying different variants of a type gave us even more possible combinations so we lost that experience we had earlier. We have to trust the numbers the EFB spits out as there is no real way to get the same numbers with a pen and paper. Now, on the bus we don't have derates (the A330 does, but i believe it is used differently than on the 737), so it has become a bit easier. On the other hand the airbus software usually gives us a range for V1, not a fixed figure and we can choose ourselves in which part of that range we want to have the V1. Using the lowest one is more go-minded, but could come close to Vmcg which can be kinda difficult to handle if there is an engine failure around that moment.
Dual independent calculation becomes very important, although quite a few companies switched to that only a year or two ago, even though there was a precedent with the melbourne case.