It depends on your skills.
If you can't complete Titan with ilvl50 gear, you upgrade to ilvl60, and if this is still too low for your char, then get to 70, 80, 90.
I am doing Caduceus with Relic and nearly full DL gear, AF2 gloves, I'm farming myth to get the AF2 robe, but just because I like its design and hate the DL cowl.
You have to have a gear that can compensate your lacks, if you are a great healer you can heal even in full AF1, no problem.
You don't have to dps so ilvl70 is not so strictly required.