A lot of this comes down to preference. I know a lot of folks preach about having a sump so you can have a refugium. I think in the size most people do them they are more or less useless (IMHO). I had a 20L sumpless, a 40B with sump, and recently relocated the 40B and made it sumpless. In just my experience alone, sumpless is easier to maintain. True, you do gotta have the heater in the DT and what not but that's up to you. Just if I was in your shoes. You already have a 60. I'd make the jump to the 125, or just stick with what you got. What I realized as I was tearing down my 40 with sump, I still had a crap ton of detritus in both the display and the sump. The way I have it setup for now, is running an oversized canister with UV. I can run filter floss in it, foam, carbon, phosban, whatever. Clean it out once a week and your done. Ultimately though it does come down to you. If you do a google search for sumpless reef tank, you will find hundreds of posts of beautiful large perfectly healthy reef systems. You could do the same and find the same amount for ones run with a sump. It can be done either way.