Technically speaking, a maxed 52 prayer zerk will be 106. At that level, you will be able to hit 445 as a maxed hit (with a c rapier).
Now, the combat levels that increase when prayer goes from 52-95 makes your account become lvl 112. If the combat levels were deducted from strength to still be 106 (so, 99 att, 83 str, 45 def, 99 hp, 95 prayer) you would only be able to hit 436). However, keep in mind they would hit more often.
So, let's say 90 att with turm is = to 99 att with regular prayers. Then the turm zerk can be 93 str, and hit 472's.
TBH, I don't think it is THAT big of difference; however, coupled with being able to hit about 30 more damage, plus having soul split, it is definitely an advantage.
***KEEP in mind that the turm % increase that I calculated was the FULL turm increase, I'm pretty sure the increase rises as the fight goes on, so in the beginning, the difference would actually be lower.