The players who haven't beat t5 are not hard core. So you can't use hardcore players to compare them.
You can do it at lvl80 or less if you know what you doing or has done it before. Ask your group if they can sit there over 6 hrs to keep wiped. If they can, you can lower the gear level. Otherwise get gear higher. Difference between 80 and 90 isn't huge but experience will cause 50% performance different.