I'd like to build a 5*+10 Eirika (the basic one, with Sieglinde): at the moment I'm stacking my copies on a +SPD -HP, but I wonder if it could be better a +ATK nature, because I think she might outspeed everyone too much with her actual IVs (like an overkill, but it's godspeed). At +10 she would be 45 speed (assuming Fury 3) without boosts. Considering what her weapon does, she might surpass easily 50 in that stat...
Any advise?