I've pressed open for years, I also strip piece whenever possible so I'm cutting through seams on a regular basis. I've found for the best results your stitch length needs to be on the small size, not tiny but not huge.
The defaults on most modern machines are a little too large most of the time in my opinion. If you can pull away 3-4 stitches at the top of your seam you need to make them a tad smaller. The Bernina I've been using for the last year fooled me at first, it starts out with a smaller stitch. But when I've made my subcuts I've been having more problems with stitches coming loose. It's not the tension, it's the being cut.
So -- next question from me, how do you put on your sashing?
I used to make columns of my blocks with sashing in-between and then a long unwieldy length of sashing along the length. What I've found works better for me is I put the sashing on all the blocks as an L shape first, then once I have the layout determined finish with the top and final sides on the blocks that need them. Then I just assemble the columns and put the top together trying to keep the pieces as similarly sized as possible while I do it. When you make the column for example, you want to put together a 3-set of blocks with a 4-set of blocks to make it 7 blocks long, you don't want to sew 1 block to 6 blocks. Your results will be straighter and it will be easier to sew.