LX and XT are probably your best buy when it comes to Shimano's mtb range and Deore was originally offered as a touring group... what you get with mtb derailleurs is a longer cage and a more robust unit that will handle greater cog ranges although there are long cage road versions as well.

Have seen many an older road bike rocking XT and LX rear d's so they could handle wider gear ranges and they work fine.

Leave the XTR and Dura Ace for racers and wannabes with deep pockets and more cash than sense... the value in Shimano parts lies in their second and third tier offerings.

As said, with front derailleurs you need to match groups as mtb and road groups have different cable pulls and will not play well together... a friction operated front lever solves the cable pull issue nicely and early STI and 8 speed groups had a friction capable front and indexed/ friction rear set up on dt and bar end shifters.