Yes. Yes I have. And you will also eventually. Even on casual you will eventually be facing end fights against giants, dragons, mindlfayers, undead doomspheres, and constructs with thousands of HPs, damage reduction, spell wards, and self-healing.
If you think random loot generated items like +6 stat items will always be OP, regardless of character level, then yes, you will eventually have less than an average chance to survive higher level content. When you actually hit that point will depend on your abilities as a player.
If you want a preview of how you might fare against higher level content, you could take your current level 10s and short-man Chronoscope on normal and see how far you get. The very first boss,
Bloodplate, has around 8,000 hit points. It is a raid, but on normal the heroic level is only level 6 and people short man this quite frequently, so I think it is a fairly good preview of what you will be up against once you start hitting level 13-14 content. I also think it is quite fun and you may enjoy it.
Another good test of your current rule set/party ability would be for your group to run the
Vault of Night flagging quests on normal. I realize you are 1-2 levels higher than the content already, but if half of you have never run these quests before they will be challenging (and fun) for you even at level 10. Some of the end fights in that chain have monsters with with damage reduction and HPs over 1000.