Wayne, the image looks like heavily modified in Gimp.
If you want to prepare a document for printing, you should convert the images in Gimp to CMYK - if it is possible.
Or you might ask your printer if you can submit a PDF X/3 file, which allows you to place RGB files directly in Scribus, and the RIP (raster image processor) of the printer will convert the images according to their requirements.
If you have a calibrated monitor you shouldn't see a big differences between an RGB and a CMYK image. It might look a tad more saturated in CMYK, that's all. But you image looks really weird to me - too much sharpening applied and a halo around the person.
Does Gimp already offer 16/48 bit image editing? If so, I'd turn it on and work in the 16/48 bit mode.