So, you pay a records processing clerk twice as much and they process twice as many records? This is what it would take to get you back to even on a cost per record basis.
That suggests they are slacking quite a bit now.
No, that is a very shallow way of trying to understand the issue.
Employees, generally, will have different speeds of getting going in the am and shutting down in the pm. Different levels of doing a bit at home and during lunch. Different levels of taking sick time, vacation and holidays. Different levels of retention. And different levels of focus during the regular day.
When the atmosphere is enthusiastic and dynamic, you boost _ALL_ of those categories. You get more hours, less training/turnover time, less sick time, people foregoing vacations, coming in on holidays, doing extra bits at home and during lunch. And focusing such that they can produce significantly more while they are in.
Failing to do these things is not slacking. But being enthused to do them can indeed double your output.
Part of this can be seen simply in the different output of a "type-A" person versus others. They are on, they are pushing all the time. They are doing extra. I believe that this employer will see people who were good before, striving to do even more now. And with the whole team doing it, one can expect, IMHO, the sum to be even greater than the parts.