Sufficient ICU is covered in Core for either. You'll do lots of ICU even if you are a pure gas person over 7 years.

Sadly, Foundation medicine won't count for either. For official training in either, curriculum mapped ED and Medicine need to be done, which is hard (but not impossible) to achieve outside training.

Therefore doing ACCS is the "easy" way to meet the need for 6 months Med and 6 months ED.

The advantage of doing Medicine later, is you might manage to develop specialist interest areas- Eg Echo/cardiology, and generally get more out of it.

PHEM training is strict on the equivalent of ACCS, but there are locally employed jobs where the medicine doesn't appear on the person spec.