No need to drop the perf book, it's all part of the planning. I've got 4 engines and a MTOW of 146.5T, and if it's a short sector I could easily be less than 120T at take off. If I can make the climb gradients, then no need to follow an engine out SID (2 engines is an entirely different situation).
I would always study the topo at heavy weights, especially if I'm unfamiliar with the area and it's IMC (yes, the engine out procedure will be flown using nav aids). If you're operating in mountainous terrain (say some Norweigen airfields), you may realise by study of the topo that the engine out procedure is taking you down a valley for example.
Being CFIT aware (especially IMC or night from an unfamiliar airfield) in a Perf A aircraft is commonplace on my flight deck
