Good advice from Otlecs as usual.

I think boxing for most people does come down to whether they are time poor or money poor. Whilst it does cost more in real cash than having multiple characters on the one account, it does mean you can achieve a lot more with the time that you can spend on WoW. From the sound of things, this is what you want to do and it should be quite simple to set up (although as otlecs mentioned, there are generally better combos, any pair is workable).

What it comes down to is whether the extra expense justifies you requiring less time to achieve your goals in WoW. Keep in mind this is true to a certain extent only however. If you want to max both characters out, then you are going to need 2 x the gold even though you are making it twice as fast. Given you are looking at a pair, it will not improve your ability to do heroics/raids etc. so again you are still generally going to need to do double the runs.

So basically, running a duo is going to allow you to do dailies faster for gold, but won't increase your maximum earning potential due to the quest cap so you just need to decide whether the extra cash outlay is worth doing this

Cheers