Go with the i7 and overclock it to the 3.2 also the i5 may be faster GHZ wise but the i7 cache buffer is twice that of the i5. Plus the Tri-Channel memory depending on the brand can be out preformed buy two channel.. I just bought 8gb of OCZ two channel pc6400 800mhz that out preforms some tri-channel.. I think they are about even but I'd still go with the i7 processor..

I'd go with the i7..sometimes you are paying for the Alienware name more than you are the hardware they put in them..