Which headphones??

Step up to the HD580/600 and you'll probably be much happier long-term, as they're much more sonically refined than the lower-tier Sennheiser models. You can pick up a used pair of HD580 (which I own now) for under $150 and the HD600 (which I used to own and should have kept: they're definitely a touch more transparent) for around or just above $200.

For context, I owned the HD555 modded to HD595 (model prior to the HD598), and the HD580/600 series is a huge step up. The lower models have a mid-bass bump and some grainy treble emphasis, but the 580/600 sounds smooth and neutral top to bottom (though some find them too warm).

Here's a great recent comparison of the HD580/600/650 series:

http://www.innerfidelity.com/content/very-important-sennheiser-hd-580-hd-600-and-hd-650

I haven't heard the T70s, but based on the graphs at Headroom and some reviews I've read, they and the Sennheisers could be wildly different sounding. I have heard the HD650, and they're very full and rich sounding, with emphasized bass and a soft but still resolved treble. The T70 has a pretty sharp spike in the treble that could be quite fatiguing. If you really want a sealed can, look at the Sennheiser Momentum (which in my book wins an award for best-looking headphone) or the AKG 550--both very well reviewed. The HD600 is considered by many to be better (more neutral) than the HD650, too.

Headroom lets you use a comparison function to overlay frequency response for various 'phones. In my experience the graphs have been pretty accurate to my subjective experience with most headphones I've heard.

http://www.headphone.com/headphones/beyerdynamic-t70.php

http://www.headphone.com/headphones/sennheiser-hd-650.php

http://www.headphone.com/headphones/sennheiser-momentum.php