8.5 works (so does 9.5). After the last update the benefits seem to be reduced a bit as adding the AQ and the new walls (and traps?) adds more than it used to, but the main idea of not adding xbows until you are capable of routinely attacking real TH9 bases in war remains solid. You don't want your defense to outpace your offense that much.
Attack who you want. If people regularly mis-judge what they are capable of doing, tell them to adjust their expectations and hit more appropriately (lower).
I mean, WHY would hitting your mirror every war be a good way to do it?



