In regard to the Maneuver Bonus provided by special materials, even the bonus provided by ithloss doesn't overwhelm the penalties of metal armor. In fact, ithloss is a special case, and one that should come with an asterisk and several other footnote symbols beside it. It's an ultra-advanced alloy created by ancient civilizations that nobody in the game environment knows how to create, repair, or rework. By definition, it's going to be unfitted... unless your character happens to be a clone of the person it was originally made for. Or a time traveler.
Okay, back to the rant about game numbers.
The penalty for a full suit of unfitted chainmail is -120, so the +60 ithloss maneuver bonus only cuts this in half, to the level of ordinary fitted chainmail (-60). If it's plate-and-chain or even full plate, ithloss loses even more ground compared to armor made of other materials. In fact, this inability to have it fitted properly makes ithloss somewhat less valuable and less useful than it really should be. And that's a real shame, considering it's kind of touted by the flavor text as being the ultimate material for forging armor.
To be honest, if I wanted to play a paladin (cleric with combat skills, or an adventurer from the Codex) wearing high-end plate armor, my personal preference would be to get a suit of armor forged from eog. No extra mana for casting spells, on top of +30 DB for the full suit? SCORE! Seriously, sign me up! And it's even a bit easier on maneuvers than normal armor... although, strangely, this bonus isn't as good as standard masterwork items (+5 vs. +10), implying that with the masterwork bonus automatically factored in, eog actually applies a penalty to your maneuvers!
Of course, you have to realize that some of the numbers in Martial Arts are just blatantly wrong (after all, they haven't updated it to the current edition), and you need to use your own judgement in such cases. For example, page 51 says a full set of soft leather armor, without improved or masterwork craftsmanship, incurs a -40 UF MaxMP and -10 UF MinMP (the current numbers are -26 and -6, respectively), and the improved and masterwork variants are based on these faulty numbers. This is not too far outside the realm of the expected, as those were the numbers being used, back in the very first edition of HARP (circa 16 or 17 years ago).