Re:
Well, it's a risk and the fitting method that I gave for 8s cassettes is designed to reduce that risk - but yes, the small contact area between sprocket spline and the valley in the casette body can be a problem. If depends on quite a lot of factors.
First and foremost is lockring tightness - you really do have to do the lockring up *tight* - 50 nm is the equivalent of 5 kg applied to a spanner a metre long - with a more typical 30 cm spanner and a real-world hand position on that spanner, that equates to about 25kg at maybe 20cm along the spanner & even if you are quite experienced, I'd definitely recommend checking with a torque wrench - a lot of old-skool mechanics like me will just put the cassette lockring tool in a bench vice and use the wheel as a lever, doing the last bit of the torque and checking it's right with a torque wrench. Users should be careful of this anyway (about 70% of the cassette lockrings I see through the workshops and on events are nowhere near tight enough, Campag, Shimano and SRAM) but it's particularly important in this situation.
Putting the turn on the sprockets as I describe, before locking them down fully helps, too.
The additional factors are if very low gears are used a lot for climbing, etc = more torque = greater propensity for sprockets to fret & damage the cassette body.
Lots of sudden change of pace - riding crits / circuit races for example - that'll mean high peak torque loads and the same problem.
If you use 9s sprockets, though, with the deep spline, and the KIT-08 spacers or the Wheels Manufacturing Shift8 kit, missing out the last cog (so on a 13-26, for instance, missing the 26), then you are using sprockets designed to fit that cassette body and although you still have to pay attention to the lockring tightness, the problems generated by the comparatively small contact area of the 8s sprocket by contrast to the 9 & 10s sprockets is avoided.
I use an 8s cassette on a 9+ body without any issues on one of my stable but not for competition - plus I am quite light (70kgs) and generally light on kit anyway ... and I have no problem but the safe option for you is probably going to be 9s sprockets & a spacer kit, and the right locking torque on the lockring ...
