You may want to test some things in SAT that are outside the IQ/OQ - that’s one difference. The other is that SAT is usually a commercially driven requirement while IQ/OQ is primarily a regulatory driven one - this may determine your approval cycle for documents and what type of documents you produce. For example, IQ and OQ are usually a combination of approved protocol (before the work) and approved report (afterwards). SAT might be a non-approved protocol and approved report - with different approval to IQ/OQ.
As an example: we require that equipment can be changed over from one product to another within a 15 minute timescale. We will test this during SAT, and our production managers and engineers will be interested in the results. We will not pay our suppliers the final installment until this requirement is satisfied. Our QA colleagues are not interested in how long or short the changeover time is - so they don’t see this work or report. They are interested in whether the change over can be accomplished without compromising the equipment’s performance with respect to the product.
If a test is done which would satisfy both the SAT and the IQ/OQ, we would normally perform that in the IQ/OQ itself, then any SAT document refer to the IQ/OQ rather than the other way round. That way we know the tests have the proper approval and oversight for IQ/OQ, and we can present only the IQ/OQ to an auditor without them having sight of the SAT.