With the original 1.8 ohm coils, you MIGHT have wicking issues with 50/50. I found that the 1.8 and 1.6 ohm coils did fine with a 70PG/30VG juice, even at a high-ish 15 watts.
The newer 1.2 ohm coils use cotton wicks, have a single, vertical coil, and MUCH larger juice channels. They'll vape 70%VG all day at 15 watts. 50/50 juice can hit 20 watts with no issues.