Barrie shoes are roomy but comfortable. Marlow wingtip is narrower by comparison. Ptb's are probably my most comfortable derby. The penny's I found to be a tad shorter overall than the other two Marlows, but still a good loafer fit.
Ben, I'm an 11.5D measured on the brannock, 11D in the Alden barrie, and wear an 11 in the Marlow wingtips, penny's, and ptb's. Don't be afraid to order a couple sizes in the Marlows, you can always send the ones that don't fit back.