Certainly not trying to start a fight here...only my honest opinion...
I haven't ever owned either a Kato SD40 or a Blueline SD40, but I have seen them both and as much as I wanted one of those sweet B&O BLI SD40's, I was sadly disappointed by the lack of details on the BLI unit. My favorite hobby store just got one in and the paint job was comparable to some "bluebox" kits!!! First I thought maybe it was just that particular one, but then some of the other bad things were lack of fuel tank detail, the windshields had the wipers molded in, the MU hoses were there (one up on Athearn) but I was again alittle disappointed. On the other hand, the sounds were absolutely un-matched and the unit actually moved very smoothly along the test track. Now I don't know too much about the Kato SD40's, but one with sound is crazy expensive, and in all actuality, I'd rather buy 2 locos without. Please don't misinterpret anything I said, and I just wanted to let everyone know what I thought. So the bottom line, if you want pretty SD40 with nice details, sharp paint, and details that (I'd guess) runs pretty good, go with the Kato, but if you want a decent loco with AWESOME sound but decent details..i.e: painted handrails, plastic grabirons, crew members, and your favorite railroad, then spend about 10 dollars more and buy the BLI unit. And unless you're a rivet counter (which you have every right to be when making purchases over $100) then you will probably fall in love with the BLI!
...Again, just my honest opinion....
-Rich