when you workout your chest, you're already over-involving the tris, so i wouldnt do tris with chest. When you're doing your back, you already over-involve the bis, so i wouldnt do that either.
How about this one:
Day 1: Chest + bis
Day 2: Legs
Day 3: Shoulders + traps
Day 4: Back + tris
or
Day 1: Chest
Day 2: bis and tris
Day 3: Legs
Day 4: shoulders and traps
Day 5: Back
This seems like a pretty solid routine. Is it ideal to workout muscle groups only once a week for optimum growth?