It took several rides before my Sidi Flex Force SRS boots broke in, 4-5. That surprised since they have the hinge. The 8's actually broke in much quicker. After the Sidi's break in, they're as comfortable as the two pairs of 8's I have. The worst part of the Sidi's is the toe needs to have the plastic above the toes continued to the sole in the front like the 8's do. The bare leather gets nicked up. Another downsides is that they are NOISY when walking around (doesn't bother me but gets some comments).
Upside's are: Easy and pretty cheap to replace the entire sole; Far and away the most water resistant boot I've ever owned (owned Oneal IFS's, Fox Forma's, MSR System 6's, tech 7's, tech 8's); Adjustability.
If I had to buy one or the other today, it'd be a hard choice. The 8's are great but the soles get torn up SO fast, they leak badly, the lower frontward closing buckle is constantly open at the end of a tight trail and the little tear drop shapes pop out after a while. I'd probably go with another pair of Sidi's. You'd think for the amount of money that they charge for either of these boots, you wouldn't have that many areas of concerns.