Keeping both phones stock (non rooted).
The score difference is due to different antutu benchmark app version (4 & 5 give different results).
Both score equally well in benchmark (18000 to 20000). But the benchmark doesn't take account of the increased ram.
I9300 has no official Kitkat support, which is actually lighter, faster and uses less ram than Jellybean.
I747m on the other hand, has official Kitkat and 2GB ram, so it takes benefit of Kitkat and 2GB ram to outperform I9300 'easily'.
Processing power.
I747m is 1.5 dual core (with krait architecture) and I9300 is 1.4 quadcore, but still I747m performs equally good in processing power, as 'krait' is a newer architecture (used in newer phones, like I9505 and G900F etc)
Summary:
1) Processing power is almost same in both.
2) I747m, with the help of Kitkat and 2GB ram takes a big lead.
P.S, I have used both of them, for few months.
