Correct. The problem you run into at smaller apertures like f8 or f11 is, slower shutter speeds, which is also not ideal for subjects that move like butterflies.
The E-M5 is definitely the answer for shooting macros with the 12-50. You can utilize the third option of smaller apertures and you can keep the shutter speeds up because the camera really performs at higher ISO settings. There's no way I want to use my E-P3 above ISO 800 for macros. I have used it at 1000 and 1250 but I think the small details do start suffering because I really have to juke up the noise filter in Adobe Camera RAW. From what I've seen, I'd have no problem going to ISO 2000 or 2500 shooting handheld macros with the 12-50 mounted on the E-M5.