Account 1 and account 3 are linked. That being said the mobs have to be green to both accounts to get x3 experience. If you didn't move you toon from account 1 to account 3, account 2 and account 3 would not get the x3 xp. What you could do is gift the lvls to account 1 from account 2. If you moved your toon to say account 6 with nothing linked to it, you would get the full x3 xp... Does this make sense?


Edit:
If i was going to create new accounts for power lvling (i might do this depends if blizzard keeps this around). Buy 2 new accounts.
Acc 1 (already have) (has a 70 rogue that i can power boost)
Acc 2 (already have)
Acc 3 (already have)
Acc 4 (already have)
Acc 5 (already have) (has 62 pally, but probably be 70 when i do this)

Acc 6 (link 2)
Acc 7 (link 3)

I could easily get these guys to 60 in about 15 days (i got 2 teams to 50 in about 30 days). Create new alts on the accounts quest them to like 15 (cause first 10 lvls are a joke and maybe 10-15 will be easy) then use my 30 free lvls to get them to 20 power lvl them in cath (it is a joke how fast you can lvl from 20-30). then use the rest of the 20/25 lvls to lvl them to 50/55. Lvl them to 60 then repeat. The down side to side is you have 2 options after the 90 days are done. Either keep the 2 new accounts or transfer all the alts on those accounts to the old accounts. Either way is not going to be cheap. Lets say that you create 4 alts, so you have to transfer 8 total that is $200 (8 x 25). The cost of 1 account for a year is $180. So the boost would be good but the cost to transfer might be a little too high.