Hiwin HGH vs. EGH

Gents,

looking at Hiwin's catalogue, I've found the following:

HGH15CA

HG / HGL Series Super Heavy Load

which are 28mm thickness, including the rail and these:

EGH15CA

EG Series Low Profile Ball Type

which are 24mm thickness, including the rail.

Looking at the specs, they seem to be pretty much identical, with the EGH having slightly higher Mr, but much lower basic dynamic load rating. The thing I don't really understand is the mounting bolt size for the EGR15 rail, which is M3 :O a step bigger, the EGR20 is M5 and compared to EGR15, the HGR15 is M4, so why the hell did Hiwin decided to go with M3, is this what causes the lower basic dynamic rating? Another thing which baffles me is the low profile HGH version, the HGL15CA which is 24mm thickness, so like a EGH, but tougher. Is this on purpose to confuse people or is there a reason for all these different carriages / rails which are very similar? Looking at Hiwin's manual, the EGH is for medium loads and HGH for heavy and super heavy, but looking at them closely, the main difference is the rail. Looking at prices confuses even more, with the HGH15CA being the cheapest, even though it's the toughest, with other 'fancy' versions being more expensive (or the same) and harder to get. Craaazy? or am I crazy and this is all standard?

Looking cheekily at THK and their equivalent for 15mm carriages / rails, I found SHS15V carriages, with rather impressive permissible moments. Am I correct to think these will rape my wallet (compared to Hiwin)?

Regards,
dsc.