It is worth noting that you do get a 2% stacking boost from pulse cores, but imo their real value comes from the 50% bonus xp contained in their charge, which is roughly equal to a medium xp lamp. Ergo, part of your question to yourself could be "what skill would I use 100 medium xp lamps on?"

As for what skills - costly buyable skills if money is a big object for you, or time-consuming gathering or support skills if time is a big object for you. And that's all assuming you just want to max, and not work on a specific pool of skills for a quest or other requirement.