I have a 1272, but I believe it doesn't differ that much vs. 1271.
Depending on screen size (and how you optimize it), I usually do a horizontal stripes and vertical stripes pattern. If the resolution with which that pattern is displayed can resolve the alternating stripes, then it's good enough. Try to go up in resolution until you hit the non-resolvable region.
My 1272 can resolve 1280x720 @ 72Hz, so I stick with that. YMMV. 720x480 is good as well since software DVD player won't do any scaling, so it's native, but I can still see scanlines with 480. My setting for cannot see scanlines would be around 660 or so (800x600 still can see a bit of scanlines).