Yeah you could try that, but damage calculations are not reliable enough. Not at all, actually. An example:Just wanted to mention that you can also use a damage calculator with the stats of the 'mons you're using to check HP/ Speed in order to check Attack / Sp. Atk. There's no need to add it to the guide because it is entirely dependent of which Pokémon you're using, its IV's/EV's, Nature, etc. It's worked fine for me so far (except with boosting Pokémon, and then again, I'm about to take care of that with Taunt lol)
Lets say you're aiming for a Modest Xerneas. (The first thing that came up with me, idc xD)
Xerneas with 31 Sp.Atk
0+ SpA Fairy Aura Xerneas Moonblast vs. 252 HP / 252 SpD Smeargle: 237-279 (75.4 - 88.8%) -- guaranteed 2HKO
Xerneas with 0 Sp.Atk
0+ SpA Fairy Aura Xerneas Moonblast vs. 252 HP / 252 SpD Smeargle: 211-250 (67.1 - 79.6%) -- guaranteed 2HKO
If Moonblast does less damage than 237, you do know it doesn't have 31 Sp.Atk. When he has 0 Sp.Atk, a Moonblast can do 250 damage at max, which is between the damage rate of 31 Sp.Atk. You can't be sure what the IV will be when doing damage.
Buckert I'm currently SRing Thundurus and I found it is useful to have smeargle hold a lum berry. Thundurus uses Discharge and has a 30% chance of paralyzing Smeargle and ruin the speed check (I use taunt first turn because I don't want him using agility and consume more turns using rockpolish). I think you should add "give smeargle a lum berry" as recommendation for SRing all pokemon with moves that cause status like heatran and the 3 beasts etc. I think it is more important with thundurus because its Prankster ability makes SRing complicated enough.
Well I haven't tried soft resetting for any of those yet since I just don't care. :p but thanks a lot for mentioning that, I'll add it to the thread right away! :)
Edit: Reshiram and Zekrom are pretty annoying as well with Dragonbreath, since that move'll paralyze you as well. Will add that right away, thanks again. :)