I don't get how you went from making perfectly good sense ("try it and just listen attentively for the sound of cones farting out") to going out on such a weak limb ("$1000 that it's not EXACTLY equal"). Honestly.
Dude, it is what it is. That's why quality control generally works withing a range, not a specific number. Think about it.
To the OP, the 210's speakers will receive damn near exactly double the wattage that the 410's speakers will receive--so go ahead and do it, but listen carefully for the sounds of speakers working too hard. Buzzing, farting, fizzing, flapping, etc. If you hear those, turn down the amp until those sounds stop. Different specific makes/models of speaker cone can take widely different amounts of abuse.
I believe we agree.
Joe.