Before I get started though let me make something clear, I am not an expert in any way, shape, or form. This is just my opinion and how I do things. Many may do it differently. And their way is most likely as good as or better than mine.
Hand stitching is not about getting every stitch exactly the same length. Experience makes you more likely to have even stitches but it is not necessary. It is more the overall effect created by the stitches, and if anyone ever comes up close - quilt police style - to examine each and every stitch then
When hand stitching with perle cotton you are not going for teeny tiny stitches. That would be counter productive. You are going for impact, enhancement of the quilt design, etc. Big is better, really and truly.
The other thing you need to do is look at the back, because if you are trying to get the stitches on the back of your quilt to look exactly like the ones on the front then you are a way better person than me. Personally I am trying to do what quilting does, hold the quilt layers together, compliment the piecing and fabrics with the stitching, create something usable and pretty.
As you can see above, the stitches are there, the pattern is there but the stitch length is shorter and the gaps between wider. It is what happens when you weave a needle in and out between quilt layers. Trust me here, when I first tried this I spent anal hours trying to make the back and the front exact. What a waste of time!
Sometimes, horror of horrors, you might not properly catch the backing layer of fabric, or just get the needle through a little bit. The world will not end. Remember, two photos up, the back didn't look too bad? Now look even closer. Imperfections abound, if you are the quilt police and looking that closely.
My other piece of advice about hand stitching with perle is to do with seams. When I am stitching something like the Christmas stars I did a couple of weeks ago I never try to get close to the seam. I go with the same 1/4" rule we use in our seam allowance. There are two reasons I do this. In my mind it looks better set back from the seam. And two, you have less layers of fabric to stitch through if you have pressed the seams in that direction in that part of the quilt. You wouldn't think two more layers of cotton would make such a big difference, but it does.
I am not sure if this blog post helped anyone at all, but if it encourages just one person to buy some perle and try it out I shall be smiling.