wireless router coverage question

Well, the transfer rate (mbps) has nothing to do with the wireless signal range.

Each antennae on a router is capable of sending out data at 150 mbps. So if you had 3 antennae you could (theoretically) transfer 450 mbps.

But the range of those signals is based on the power of the transmission provided by the router's components. I have had little faith in the marketing hype provided by manufacturers because there is no quantifiable measurement in a router's specs that would indicate a unit with greater signal power. And since all communications devices must conform to very narrow operating standards I don't see a lot of room for improvement as far as one device over another anyway.

I generally depend on product reviews, even though I know these reported results are anecdotal. The range of any wireless device is much more affected by the environment it is operating in than any small difference in transmission specs.
If your router and desk were set up in a cow pasture in the country you would get excellent range. Set up the same router and desk the same distance apart in a crowded apartment complex with steel stud partition walls, lots of wireless phones, and lots of other wireless routers and that range would drop off dramatically.