That's an interesting variation to explore.
But there are more two systems that may be compared:
1. Differences between two alphabets, such as English and Greek.
2. Differences between alphabets that represent vowels and
those that typically omit vowels, such as Arabic and Hebrew.
3. Differences between alphabetic and character systems, such
4. Japanese, which mixes two systems, characters (kanji) and
In addition to the psycholinguistic evidence, there's evidence from neuroscience: Which areas of the brain become active in reading, writing, hearing, or speaking languages with those systems? What differences are found for the different languages of bilinguals? Which functions are impaired by strokes or other brain lesions?
For bilinguals, strokes in different areas of the brain may have different effects for L1 and L2.
In Japanese, a stroke in one area may cause a patient to lose the ability to read kana, while still reading kanji. A stoke in a different area may have the opposite effect.
After a stroke, a patient may recover some abilities faster than others. What are the differences, and how can therapy help?