Hey girl, I'm 5"1 and I have both speedy 25 and 30 and I am perfectly comfortable with both of them. I love both sizes, although, for an everyday bag, I would prefer the 30 better personally. The only problem with the speedys is the sagging bottom, so I overcome this by putting a cardboard on the bottom of the bag to maintain shape. I have yet to try a purseket, sometimes things are a lil messy inside my speedy, I can imagine a purseket will be a suitable organizer for all my junks.
At the end, height doesnt matter. I have a friend the same height as mine who can pull of the birkin bag in the 35 cm size, I cannot, as I think it looks too huge on me, I can only do the 30 cm.
With you, you feel the 30 is too big, while I'm not, it's great to see these differences, huh?
If you want pics of the speedy 25 and 30 side by side, just lemme know okay