I have dozens of sites which get that much traffic and more, yet some are not even ranked that high by alexa. Hell I have sites, which are listed in dmoz, yahoo, and google at the top of the serps, and according to Alexa they rank in the 8,000,000 range. :laughcry:
If you wish to rely on Alexa thats your perogative, but IMO it is not a fair guage of traffic, only a guage of Alexa users who visit your site.