I just finished fighting this as a 42 PLD/RDM with my lvl 38 attacker NPC
Now i know NM's are tougher than monsters the same lvl as them, but I only just managed to bet this with about 40 hp and 3 mp remaning! This makes me think the NM must be around lvl 42, perhaps higher!
I took RDM as sub, mainly for the spells i knew i'd get, En-spells, Blaze Spikes, Aquavel, and I dont think I'd have beaten it without them. I couldnt get a silence to stick, so I decided not to waste my time. I Shield Bashed it when it was preparing some crazy aga II spell (didnt stop him hitting me with a different aga spell 2 sec's later ^^)
Anyway, he was hitting me really hard considering my defense and his magic was quite devastating, but i managed to hold out, SC'd with my NPC and then got dropped to about 10% health whilst he was on 33%. I hit invincible, then laughed as he aga spell'd me again dropping me to 20/770 HP /panic! Luckily for me i got 100% TP just as invicible wore off and i Fast Blade'd him to death!
Just to let people know this is doable at lvl 42, but it was dam hard.
Happy Hunting!