Ask the school. They're the only ones who could possibly know what they'll do.
At the higher ends of IQ and OLSAT, OLSAT scores aren't well-correlated with IQ. (So if you take the kids who score above some percentile on the OLSAT, and give them a full IQ test, the highest-scoring kids on the OLSAT won't be the highest-scoring kids on the IQ test, and vice versa.)
OLSAT E is the 4th-5th grade version; F is the 6-8th grade version. I'd be surprised if they tested rising 6th graders using F, rather than E, but the school is the only one who'd be able to answer that.
