Note: the following is a direct quote of research posted on wowhead.
Everything stacks normally EXCEPT these exceptions:
[Cat Form] speed increase is ignored while under the effects of [Dash].
Enchant Boots - Minor Speed speed increase is ignored while under the effects of [Stampeding Roar].
[Prowl] is always applied last. [Ex: Minor Speed + Feline Swiftness + Cat Form + Prowl, 108 + 0.15(108) = 124 + 0.25(124) = 155 - 0.30(155) = 109]
NOTE: Does not affect [Aquatic Form] or [Flight Form] (flying), but does effect Flight Form at ground speed. Guild speed buff affects Flight Form while flying, but not on the ground.[1]