obscura's get to 14"-16" normally but there are reports of 24" in an aquarium! striata get's to be 36" give or take a few inches,but there is one population that only grows to 24" (unless it turns out to be a different species!)
The books say 35-50cm but 35-40 is the norm for obscura's . As for striata It can grows up to 90cm(a lot of books say 1m) the bigest one i have had was 4 years ago it was 26" this species is sexually mature at 30 cm but as i said grows to about 90 cm / 35 inches