When you’re shooting sunrise/sunset images you pretty much have to accept that if you want the sun in the frame it’s going to be blown out and cause lens flare. You’ve done as good a job as is likely possible in controlling this.
Your ten stop ND filter isn’t going to help balance the image because it just makes the whole thing darker. An image like this with a clean horizon line is just screaming for a 2-3 stop hard edge graduated ND. If you’re not familiar, a grad ND is a rectangular piece of glass with a tint that only applies to half of it. This allows you to darken the sky while keeping the foreground bright; thereby reducing the dynamic range of the scene and improving your cameras rendering.
Using filters for this trumps HDR processing because it just looks more natural. The downside is that a square filter holder and a couple grads can easily cost $400+ and cheap options generally have severe color casts.
My personal preference when shooting sunrise/set is to keep the sun out of the frame altogether. There are two ways to do this:
1.) Shoot with the sun just outside of the frame to the left or right. You can still get great images with colorful sky, but you avoid having the blown out sun or lens flare in the image.
2.) Shoot just before sunrise or just after sunset while the sun is below the horizon line. This is generally when the colors are the richest anyway, so it is my preference.
Sorry if I rambled on a bit or got off topic; it just sort of spilled out. Hope some of this is helpful.