I was thinking strictly in terms of his own abilities, but you make an excellent point that I hadn't expanded my thought process to include.
I don't agree with MB being captain if Boca is on the field. Unless Boca is subbed on. Boca knows full well that he is an aging veteran and his time as a pro athlete is coming to an end. If he is on the field we need him to be confidant. If the arm band is stripped from him it could damage his confidence (even if it is very subtle blow to his confidence it could still hurt the team). Essentially, I don't see a lot of upside to MB being captain over Boca (if Boca starts)... but there could be a little downside. If it was me I wouldn't switch captains in this important match. Since MB seems to be in the role of captain in the last few days, I would guess this means Boca isn't starting.
If David Beckham can suck it up and play for England after not being captain, Carlos freaking Bocanegra can be a professional and suck it up if it's what's best for the team.
My point is it might not be the best for the team on this day (again if Boca plays). David Beckham is an anomaly not the norm. I don't know his circumstances for England... but I imagine at the time Beckham wasn't playing for a 2nd tier relegation team in Spain. I would imagine Bocas confidence might of taking a hit already.
during the friendly vs Brazil in 2010 he got the armband after Boca and I believe Donovan were subbed off (maybe even Dolo don't remember), I think he may have gotten the armband in the second half of a game in 2012. Jones being named Captain for last year's camp cupcake was more Jurgen trying to calm Jones down and show confidence in him and JJ even admitted it helped him figure some things out. For now though, it's still Boca's team. Mikey is without a doubt captain material but there's a reason why Boca pretty much has gotten the armband wherever he has gone in his pro career.