1. They won't provide you a duty weapon?
2. The following is my opinion of the two. Others will vary. Either would suite me for duty use but I do have a preference.
I hate RTF of gen4. In an open duty holster being occasionally banged against a wall, door frame, ect. those little dots do get easily damaged. The same kind of use I never saw the kind of finish damage to the gen3. Also I don't understand who exactly had a hard time holding on to their gen3 guns in the past. I've held and shot mine with cold and soaking wet hands and no problem. RTF is one of those solutions to a problem that doesn't exist type things.
Concerning the new RSA, I can't tell a difference in recoil over the previous gen3.
Concerning interchangeable backstraps, I didn't have a problem with the grip circumference of gen3 so that is not an issue either. If you are small handed then the grips might be worth it on the gen4 for you.