A flying diamond for example, isn't really practical with a cat cut ridgeline, but with cat cut edges it works like a charm - it's just a matter of tensioning the tarp right. It may take and extra minute or pass around the tarp pulling your guy outs tight one more time, but once it's set up, it stays tight and quiet through the night. Mikeinfhaz is dead on with the 'sil forms it's own false cat ridgeline' - the stretchyness of the fabric really lets it conform to how the wind is blowing it and how the guyouts pull it.
6FO: Try adding the three inches to the length of the tarp, then cut the curves. You keep the benefits, and don't lose much (if any) coverage. Although just doing the long, parallel to the ground sides of the tarp should still give you most of the benefits of the catenary cut. The 'short side' curves really come into play with angled cuts like in a hex or other shaped tarp or with non A-frame pitches. But they still help with the overall guying out of the tarp, especially the area near the corners.