Confused about elixer

So I'm confused on how the speed elixirs work. For example lets say you have 3.00x ms and use the +25% for 40k gold it will now be 3.25x ms and if I were to do the same with t+30% speed elix from auction with gold my speed would stay at 3.00x. what's the difference

Also a question on stacking. Also stacking and ones that don't stack when I have 3.00x ms and I use a pet that has 30ms(stacking) it becomes 3.30x but if I were to use a pet that gave me 25 movement speed wouldn't that mean 3.00x (25%) =3.75 but it would stay the same at 3.00x.

Also the 25% movement speed from store is missing a +25% meaning its stacking. And also mentions that we get a 25% movement speed bonus but we get 25% ms stacking instead.
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just confused no hate.

If it's stacking means it adds up to your total ms, easy. If its not worded with stacking then it still adds up but it gets overridden by your highest non stacking speed source which is your speed set. Everything that's stacking speed will add up to the highest non stacking speed number you have.