P7M10 is a real klunker compared to the 9mm versions. H&K made the M10 capable of handling the 40 cal round by adding significant weight to the upper portion of the slide. It's heavy, looks wierd, and has a lot more rotational recoil force when fired because of the high weight.
OTOH, my P7M13 feels good in the hand, although not as quite as sleek as the M8's or PSPs, shoots great, and is a real tack driver out to 25 yards.
There are a lot of 40 cal pistols out there that feel, look, and shoot better than the M10. H&K just wanted onto the 40 cal bandwagon before they came out with their newer models like the USP. It died a quick, quiet and merciful death on the scrap heap of unique, but strange weapons.
I'd be stunned if there is actually a stainless version - it's probably a nickel piece that's mismarketed. To my knowledge, H&K never made a stainless P7 in 9mm or 40 cal.