It was really a generic question, I was using the case of a window opening as an example. But I do have a pending project where I need to cut openings in 4x8 material, the blind cut is within the FSK 420's capacity.
The HK saw is really attractive to me, it seems to address all the things I hate about my "ordinary" circular saws that it would be at least partially replacing. The decision for me is getting just the saw and FSK 420 to start with or get an FS track too (or instead), either way, it's awfully dear compared to those "ordinary" saws, but I hate trying to do good work with the usual combination of clamp on generic guides or framing lumber. +I have projects coming up where the cost of spoiled materials could make the saw seem cheap. Thank you again.