Thank you all for the tips.

Maybe I was not clear in my OP (English is not my native language) : Heroics are not a problem anymore, I have quite a few on farm (UK, Nexus, Culling of Stratholm, Drak'tharon, Gundrak, HoL ...). This enables me to gear through badges rather rapidly. That's why I expected the first raid in order of difficulty to be rather ... easy

According to Furshpere's link (www.wow-heroes.com, great site, thanks), my team basically over-gears Naxx. So the problem is not here.

I guess it all comes down to strategies and practicing, then.

*heading to tankspot*