I would not be buying now. KMR hit $54.66 on the close 8/8/11 and is now $66.33, more than $11.50 higher -- that's 10 quarters of stock dividends higher. KMP same thing with a $64.58 August low and a $76.36 price now. The price you pay for a stock is the best way to control you risk. These are toasty highs for KMR/KMP, I'd wait.
KMR is 21% higher ($66.23/54.66) and KMP is 18.2% higher ($76.36/64.58). This emphasizes the point that KMR does better / the discount decreases when KMP/KMR goes up. This will reverse if KMP/KMR goes down. If I had to pick a direction, I'd say down, so you would want to buy KMP to lose less.
KMR had a compelling "yield" of 8% at prices under $57.50. KMP had a compelling yield of 7%+ at the August low. Where where you then??? I'd wait for KMR/KMP to get to these yield levels to yield the same but on the new $5 distribution projected in the merger announcement.
If you can unravel all of the moving parts in the EP takeover and from that figure out that KMP/KMR are a buy/buy/buy you are smarter than I am. Deal won't close until 2012, so I think some of the froth here may send prices lower.