Although the trend is the other way at the moment (perhaps credit goes to Rick for that) the chance of a UDRP attempt to take away a valuable domain like this is a lot higher than less obvious targets. If you put that much money into one domain I suggest you build a Bonafide business and get your own trademark.
I also agree with the above poster that a diverse portfolio is more sensible. But there is one thing more - You can get an idea of LL.com pricing easily enough. But there is huge variation in those prices, one reason is quality, the other, at least as large, is the pure randomness of a tiny, highly inefficient market.
With that kind of money I would go for three letter .coms, some lower value, some higher. But first learn why prices are what they are (Letter-quality, pronounce-ability, meaning). Domains are not like stocks where the clueless still have a chance. 98% of domains are junk, 99% of what is not junk is priced for the eventual user, not the domain investor.