Do unique passive buffs from different items stack?

Many items have UNIQUE Passive: Some Description as a part of their description. I understand that UNIQUE implies that you cannot have 2 of the same item with the same effect.

What I am not sure about and haven't found information about is whether you can stack SIMILAR UNIQUE Passives.

Boots, for instance, may have Increased Movement Speed 2, or Increased Movement Speed 3 (among other things) as UNIQUE Passives. Does that mean that I can wear both and receive the benefits of both, since they are not identical? (2 vs 3) Or since they affect the same stat, do they not stack with each other?

I haven't been able to find clarification on that point.

Solution 1:

Boots are a specific case. You can't have more than one movement buff from any kinds of boots at all.

As for other items with UNIQUE passives, as long as you don't have the exact same item, they all stack on top of each other.

Apparently, there are other exceptions as well. From the wiki:

Unique effects that do not cumulate among differents items include Movement Speed effects from boots (only the best effect applies), proc effect of Sheen, Lich Bane and Trinity Force, and the mana gained from Tear of the Goddess, Manamune and Archangel's Staff.

Solution 2:

It's worth noting that any champion with a unique friendly aura item (Zeke's Herald, Will of the Ancients) can additionally receive that aura from another champion. This is why double Will of the Ancients is so strong and common, the owners of those items get double the effects of the buff when near each other.

http://leagueoflegends.wikia.com/wiki/Aura