Ummm....Ok im trying to understand your question.......By Sony Vaio 15.5 inch you mean a laptop, Just to put it out there some laptops GPUs are not upgradeable unless its a Gaming laptop that was meant to be upgradeable in the future plus changing CPUs on a laptop would mean a whole new Thermal level so it would cuz it to run hotter, So you need to check this 1st. For FSX, it would be better on a desktop computer due to airflow and higher performance plus the availability to upgrade and accept all types of GPUs, But the i7 is a mobile solution which means is a lower clock but should be able to run FSX not on ultra or high but maybe on Med to Med-high settings and that GT 735 should be fine,
Hope I was helpful to your question