Was the 'Mithral Fullplate/Heavy Armor Optimization Feat' questions ever settled?

[TheEvil]

It has been several years since I played D&D 3.5E and I don't recall if the following debate was ever firmly settled:

A fighter with the Heavy Armor Optimizatin (HAO) Feat (+1 armor bonus, reduce check penality by 1, Races of Stone) finds a suit of Mithral Full Plate (counts as medium armor for movement and other limitations per the DMG). If the fighter wears the mithral fullplate, does he benefit from his HAO feat?

 

[Nebten]

I don't know if the dust was ever offically settled on this, but here's what the FAQ says:

Is a character proficient with light armor, such as a rogue, considered to be proficient with mithral breastplate?
What about a character proficient with medium armor, such as a barbarian—is he considered proficient with mithral full plate armor?​

The description of mithral on page 284 of the​

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DMG is less precise than it could be in defining how it interacts with armor proficiency rules. The simplest answer—and the one that the Sage expects most players and DMs use—is that mithral armor is treated as one category lighter for all purposes, including
proficiency. This isn’t exactly what the DMG says, but it’s a reasonable interpretation of the intent of the rule (and it’s supported by a number of precedents, including the descriptions of various specific mithral armors described on page 220 of the DMG and a variety of NPC stat blocks).
Thus, a ranger or rogue could wear a mithral breastplate without suffering a nonproficiency penalty (since it’s treated as light armor), and each could use any ability dependent on wearing light or no armor (such as evasion or the ranger’s combat style). A barbarian could wear mithral full plate armor without suffering a nonproficiency penalty (since it’s treated as medium armor), and he could use any ability dependent on wearing medium or lighter armor (such as fast movement).
The same would be true of any other special material that uses the same or similar language as mithral (such as darkleaf, on page 120 of the ECS).

Therefore, I would have to say it counts as Medium Armor and thus it wouldn't work with HAO. Otherwise you would be having your cake and eating it too. Luckly it is clearified in Pathfinder and in PF it would count for HAO. So do what ever is most fun.​

 

[domino]

The SRD says Mithral Full Plate of Speed is considered Medium Armor, so I'd say they probably don't technically stack. Mithral Full Plate of Speed is not the exact same thing, but nothing in the description says or implies that it's medium armorness comes from anything other than being made of Mithril.

 

[Visigani]

Mithril Fullplate, as mentioned above, is not heavy armory and so would not benefit from a feat that applies to heavy armor. Barbarians, for example, can use Mithril Fullplate without penalty.