Hi,
When you power up AP-225 from 802.3af there is no sufficient power to run all three streams for 'n' radio. In my opinion, at 2.4GHz there would be no significant difference between APs. The real performance in 2.4G band would be similar at any AP. BTW, there is very limited number of 3x3:3 adapters (2.4 and dual band) on the market ;)
Many regards,