captain I’ve played DS games on the DSi LL, 3DS XL, and new 3DS XL and I was able to enjoy using all three. That being said, due to differences in resolution like you mentioned (400 × 240 and 320 × 240 for the 3DS, 256 × 192 ×2 for the DSi), you will have to put up with some non-integer scaling to really use those large screens by playing full screen. I took some comparison shots, if you’re interested:
As you can see, the 3DS (right) is significantly blurrier, but totally playable. If you want those eye-pricking pixels, though, you can’t go wrong with the DSi XL/LL
