The chain on all three models is the same 101 link, 530 size chain. The difference is in the countershaft sprocket. the B5 and C5 comes with a 17 tooth sprocket, where the C5 has an 18 tooth sprocket because of the wheel size difference.
An Oring chain will fit on a C5, but will not fit on a B5/G5 because the wider chain will hit the countershaft bearing boss. So, if you want to put an Oring chain on a B5/G5, you have to go to an 18 tooth sprocket.
Frankly, as far as I'm concerned, the stock chain on the B5/G5 is garbage. I took mine apart after 6500 miles after noting the gigantic droop spoken about in another post. The internal bushings were breaking apart and were just split bushings to start with. Absolutely, the lowest quality chain I have ever seen. When those chains start breaking up like that, the "stretching" also destroys sprockets. So if you like replacing chains and sprockets every 10,000 miles, or less, have at it. I'd rather spend my time and money that will last considerable longer and not require adjusting literally every time I ride it!
The C5 Oring chain is obviously a better quality chain than the one on the B5/G5, hence the longer life.
I went for a mid range Tsubaki Oring chain for about $100 which I'm sure will take me, from past experience with these chains, to 30,000+ miles and the sprockets will go there with it.
There are other high quality chains that are really good including RIK, DID, and Tsubaki, etal. Xchains, as mentioned, will last even longer, but cost more.
Don't consider RE the only bad guy that cheaps out on OEM chains. Most manufacturers do. I had a Regina chain on a Triumph Speed Triple that lasted 8000 miles and Regina does make some good qulity chains. I've have had some pretty short lived chains on Hondas, too. It's pretty common practice.
I wouldn't base the decision making on buying the C5 or B5/G5 on the chain. Neither chain is worth arguing about.
Bare