Quick Dex/Casting question

We have seen the video comparing 14 dex to 45, and the difference is huge.

https://www.youtube.com/watch?v=ynX3nOHDhCA

And we have seen the other video comparing every level between 31 and 46.

https://www.youtube.com/watch?v=yHfPcu_B0nQ

...but I also read on a forum, (can't find a link to it), that 8 through 30 are the same and that the speed bonuses don't start kicking in until level 30...Anyone know if this is true, tested it, or seen a test, or is it just another unfounded forum "fact".

I have 16 dex to wield my darksword and am wondering if it would be a total waste to bump it up to 20 or 21, in an attempt to speed up Great Combust a bit.

I have tested this and it is such a small difference its not even worth putting points into dex. I personally say go 35-45 or don't go dex at all.