It depends on whether you are zooming in on the images or not. If they are static, then you don’t need any more resolution than that of the sequence it’s sitting in and in fact you’ll get a better downsample in Photoshop, not to mention saving system resources in FCP. If you are zooming around, figure the smallest frame you want to see and adjust the image size in Photoshop to make that area have the same resolution as your final FCP sequence. If you do this, you won’t zoom past a 100% crop and cause uprezing pixelation.
John.
https://www.lyric.com/fcp-plugins/