personally, I like 6 1/2 inch squares for my eye spy blocks...mostly because that is the width of my ruler 61/2 x 24 inches. I use a 2 1/2 inch strip of sashing fabric with a 2 1/2 inch corner stone block.
If you purchase a quarter yard of novelty fabric, you should get 6 nice fussy cut blocks for your quilt or to share!!
jodi