I'm not sure how much snow you get at your location or how you handle it. If you use a plow, sooner or later, you're going to plow up those 8" cinder blocks. Yeah, you can mark them with stakes but they're just something else to maintain.
They are also difficult to mow up against. You wind up using an edger or string trimmer which adds to your lawn grooming time.
I gave up using hardscape borders on my gravel driveway years ago for these reasons. I now use a shallow drainage swale instead. Much easier to maintain.