hmm... 5 runs through deadmines with boosting means you have to sell tons of grey worthless trash you've looted. Sometimes you can't pull the mob packs together and get them down so you have to run forward and back too loot everything. In the end you have to sell all the grey trash to the vendor to continue and trade all the useful stuff to your toons because your bags are full. Then head to the auctionhouse, try to get rid of all this stuff without knowing about the transmog worth of every item which means lots of trys to get it sold while having the auction house fees. In addition he got time ticking against him because his RAF time is running out (14 days left) and he has to get the group to 80.

in the end you have :

the chance of getting a rare item you can sell for 1k+ (but only if you know that this item is that much worth and don't trash+cash it for 5 gold at AH/vendor)

vs

getting to highlevel several days earlier which means you can start doing dailys as a group and get $$$ or start running old raids solo to grab transmog gear
or farm cloth out of Naxxramas which is worth 50-100 Gold / Stack on my realm or farm pets out of raids which sell 500g - 25k / each on my realm.

I'd take the second option