Mountain Loop Hwy does not cut though to Hwy 530 any more (it used to). But a storm a few years ago washed out a section of the road between Barlow Point and the town of Darrington - that section was unpaved gravel road to start with. So Barlow point is as far you can go on Mt Loop. If you are time constrained, I would drop Mt Loop. The highlight of Mt Loop is the Big 4 Ice Caves and in August, the ice caves most likely will not be that dramatic. Secondly, the Big Four mountains (where the ice caves are) are best viewed in the morning. Thirdly, it's about 90 minutes from Seattle and if you pass by Seattle again, it's not too hard to reach