I've just completed a real world test for me between 4x5 and 8x10 formats. One 4x5 Linhof Technica with 150mm lens and one 8x10 Sinar P2 with a 300mm lens. Side by side at the same lens height focused on the same part of a very detailed urban landscape (buildings, trees, cement, piles of dirt, signage, tarmac, cars and people). Both cameras were on large tripods and fired simultaneously with cable releases at the same exposure time and f-stop.
The film was Provia processed at normal. On the light box the 8x10 looked a country mile better, particularly through a loupe. They were then drum scanned to 100mb file size, reduced in file size slightly and printed at around 16"x 20". I would have put money on the 8x10 being a clear winner.
The difference in resolving detail and sharpness was so marginal that I can barley tell the prints apart. There is zero grain in both. It's only when I study the most minute detail through a print loupe that I can pick up some of the differences.
I also shot the same scene with my EOS 1ds Mk II. The large format film makes the 16MP image look absolutely rubbish.
My test is by no means scientific (the lenses are different, the cameras are different etc etc etc) but it's how I operate - on location, scan at manageable sizes and print on inkjet. Others operate differently by scanning at huge sizes and printing on massive Giclée prints or by printing in a darkroom but unfortunately I don't have the time nor money for other processes.
I'd never really bother writing about this but I'm truly staggered that there's no noticeable difference in the prints. I'd love to here from anyone who has conducted a similar side by side test.