I have the MI424-WR rev. I router and my wireless speed is typically around 80Mbps when my notebook is in the same room as the router. In the living room, with 2 walls between, wireless speed is typically around 50-55Mbps. (75/35 plan)
Keep in mind that when moving away from the router, your computer's wireless card is also a big factor in WIFI performance. Stats above are for a new WIN8 high performance notebook. I have an older notebook that only gets 40-45 Mbps.