First of all, a disclaimer, I am a production turner, and individual results will vary.
Medium curved blade of the standard McNaughton coring blades will do fine but your lathe may not have the torque/horse power to run it efficiently, same with the Oneway. The Mini McNaughton set would work better, and have smaller points so you don't need more horse power. However, I can shape the outside of a bowl much faster with a big heavy scraper than I can by using a coring blade, if for no other reason than it is one extra set up of a tool to do. Having a curved bowl tool rest will save you as much or more time. On bowls the size you are turning, by the time I core it, and then finish turn the inside of the bowl, there is little or no time saved. On blanks that size, I would expect to get 3 to 4 bowls total. Some times the last bowl is too small to be worth the effort. The major time saving is in turning the core. The outside is already shaped, you just have to clean it up, finish cut, turn your tenon or recess and reverse. I doubt that you will save much time with a coring system, at least until you learn to use it. The Woodcut system is great for bowls that size, and is priced right (cheaper than the Oneway, and a bit cheaper than one set of the McNaughton blades), but it isn't suited to coring the outside (neither is the Oneway). The big blade on it is a 5 inch radius, and I have found that it works better on the smaller lathes than the Oneway, but not better than the mini McNaughton. You will need higher speeds for it, or any coring system on your lathe, in the 600 to 800 rpm range. 500 rpm will work, but you will have to go slowly. I prefer the McNaughton because it is a lot more versatile, and after you learn how to use it (there is a learning curve with it), it is faster to set up and use.
robo hippy