The DT1350s and the M50s might not be for your preferred sound signature, as both have a bit of treble emphasis that may seem fatiguing if you like your A151s. The MS400s are warmer, and may suit you better, and I would also recommend looking into the B&W P5s (Though they are a little pricey). The P5s are priced a little high, but they make up for it in usability, with very good isolation and comfort (esp. given they're on-ear), portability, and a nice warm sound signature.
Also, the 598s and K701s are open (though you probably know that), and will leak sound. Also, the K701s will definitely need the E17 or something similar to amp them for portable use. From what I've heard at least, the 598s might give you more the sound you're looking for, and aren't quite as amp-dependent as the K701s.
I forgot to add I also managed to give the P5's a try out for about 5 minutes as well. It was quite short but my initial impression was it was just too muffled sounding and not where I wanted it. I was only able to listen for about 5 minutes though, so it isn't entirely fair to pass total judgement against it. I definitely agree with that they isolate very well and are very comfortable. The price was a bit of a negative though as you said. It isn't much more than say a 598 or a K701 but I get an impression I'd get more of my moneys worth from those or even some others. I've been reading more reviews of headphones and I've come across another pair that I was thinking might be to my liking which are the Denon DN-HP700. I might just get a cheaper portable for when I'm on the go as I still have reservations of it might be too open for others even though I've asked with the Grados when I had them and people didn't notice them, and then have the open for home. I already know I'm not going to stop at one pair of headphones by any sort...
I did notice in the review it says if you are sensitive to the treble to beware, but from what I read it doesn't give me the impression it would be as bad as say the Grados in terms of brightness or fatigue. Something will have to give somewhere and I'll just have to go with a pair.
Edited by jotry - 1/16/12 at 6:53pm