I have both the f2.8 and f4 Nikkors and apart from the fact that the f2.8 is clearly brighter for focussing, I'd be hard-pressed to tell the difference between them at the kind of enlargements I do (up to 11" x 14"). I only ever use a glass neg carrier for 2 1/4" square by necessity and find it a right pain. All those extra surfaces to collect dust and the occasional print that shows Newton's rings (despite the glass manufacturer's insistence that this is "anti-Newton's ring glass") leave me doing my utmost to avoid complicating matters even more by using glass for 35mm printing!
Steve