I have not used either sharpening medium you list, but 0.5 micron is roughly equivalent to around 30K grit, so I would suggest that, other things being equal (like you have created a good bevel etc) the 0.5 diamond would produce what feels like a sharper edge. James.
I can't give you the scientific facts to prove my opinion. I can say that a 12K is for polishing ad I personally love my Naniwa. Sharpness is determined in the lower grit hones, the higher grits are for polishing. The pasted strop is also a polishing tool as well and probably will improve the smoothness factor slightly beyond the 12K. However, you can get a fine shave straight off the hones with less than the 12K or strop. If purchasing, the strop is probably a little cheaper (?), but if you have a solid 8K hone, you can make a simple strop for paste and get really nice shaves without the 12K. On a side note, I personally use the Nani 12K and the a CrOX lightly pasted strops for about 5-10 laps. Then I go to cotton and leather for about 50 on cotton and 100 on leather. From then on I only do about 30 laps on the leather before each shave. I don't know if this helps, but I tried.
For what my two cents are worth,Ive used gssixguns method,found here some where and got the shave of my life with just an 8000 Norton linen,then leather. I posted this under "I got it",and that gave me the confidence to take on my boker which just gave me an outstanding shave,Id say just take your time with whatever your using to polish your blade and then strop,man strop......
You can't exchange the sharpening properties of *any* strop (creating a smooth second bevel) with *any* stone out there. I ( and many, many others) use a pasted strop (mostly chromium oxide) as the last step before the leather regardless of which stone we used prior. But that's the european approach, I know many guys from the Americas only use hones. Each to his own as long as the shaves are okay.
I use a set of Naniwas, with 12k being the highest, I can shave off the 8k, but use the 12k for smoothness. I then go to the leather. I try to keep things as simple as possible.
