I don't really see the point. And I say that as someone who owns both an iPhone and an Android device. Any modern smartphone with a fast processor and capacitive screen should afford, for the most part, the same text input speed. The virtual keyboards on 3.7" screen smartphones are generally all the same size.
I find the 4" screens slightly easier to type on (4.3" strikes me as stepping into "a little much" territory in terms of phone size) due to there being just that little bit of extra space which makes the input a little more accurate and doesn't require as many corrections. I actually find most predictive text in English to be slower since for unusual words, having to manually type in those words with long-presses kind of breaks up the flow. But I type very fast on phones though, so maybe that's just me.
I find predictive text to be quite useful for other languages though, particularly for ö,ä,ü,ß, etc. Predictive text is generally right about spotting words where an "o" should be an "ö" and suggesting it as the top result. That winds up being quicker than long-pressing the o,a,u, or s every time I need a special character. So predictive text that only corrects if you select the suggestion (not simply auto-selecting the top choice when you hit spacebar) is generally the quickest for multi-lingual support. So generally for anyone who speaks another language in addition to English, using the other language's keyboard with predictive text makes for the quickest input, since for the English words we just type them in manually and for the other language rely partially on predictive text to speed input of special characters.
That's just my experience, although many colleagues who are bilingual made the same observations and generally utilize the same philosophy for text input.