I noticed a huge difference on the squat and deadlifts with the belt with the working set weights I'm at now! I have a 3" belt and it happens to fit nicely right in between my ribs and my hips (not a lot of room to spare, though).
On the press, I don't have fractional kg plates, but I do have a set of fractional pound plates (I tried to order a set of the fractional kg plates from the guy on this forum but he never responded to my PM), so this is 1.25 pounds on each side of the bar, 2.5 pounds = 1.136kg. I had 20kg bar, with 12.5 kg standard kg plates (5kg and 1.25kg on each side) and then 1.136kg of my fractional pound plates.