I am not recommending one or the other but do prefer SRAM to KMC, from experience (9sp).
The specs drawn from
SRAM site for 830 and 850 cassettes are identical: even down to the colour (silver). I suggest you might adopt a more enquiring dialogue with your 'techie folk'.
All below Hal fords!
"The
SRAM PG830 8 Speed Cassette 11-28 is great for off-road use with a steel lock ring and chrome plate sprockets.
PowerGlide II cassette technology optimized for MTB. More reliable. More durable. Better performing, thanks to an optimal tooth profile and shift ramp design for quick and positive index shifting. Steel sprockets with step-riveted pins for strong side plate retention ; 276g.
"The
SRAM PG-850 8 Speed Bike Cassette 11-28 with race-inspired Powerglide II technology is light-weight and durable. Make the most out of your bike with a great quality cassette and race your way to first place. [It] has been designed specifically for mountain biking. It is more dependable and resistant, and it provides high-level performance due to an optimized tine profile and the design of the shifting ramp for quick and efficient gear changes. Chromium-plated steel sprockets with step-riveted pins; 276g."