Well the circumference of a circle is Pi * the diameter so assuming your sizes are the diameters, your first table is 113 inches around and your second is 132 (nearly). 113/4 = 28 (just over)and 132/6 = 22(nearly), so your smaller table gives each person 28 inches and the larger only 22. A 4ft table has a circumference of 150 (just over) so divided by 8 gives 19 (just under) so you'd need a 5ft circle to fit people with slightly more elbow room than 6 (23.5")
The Winchester table gives everyone 28 and a bit inches so enough room to throw your chicken bones over your shoulder with room to spare :-)