You could also set up a control logix bridge with a 1756-enbt, 1756-dh485, power supply (1756-pa72),a 4slot rack (1756-A4??), and an ethernet switch.
With this you could keep your ethernet intact and also be able to get to your 485 HMIs and PLCs across the ethernet. I have not done this on DH485 yet, but have done this on DH+, and it worked great.
No contol logix processor is needed, therefore if you don't have RS5000, you won't need it, all you should need is RSLinx.