Build quality:
T1s feel a bit more robust mainly because of the weight, but SA5ks are as nicely built as the Beyers. Cable is not as robust, but it is still very nice and seems extremely durable.
Sonys really look like a piece of high-end gear (cosmic era) while T1s have that casual, classic look. Both very attractive.
Comfort:
T1s much heavier and in the beginning one might think less comfortable for longer listening sessions, but their earpads are more comfortable than the leather on Sonys. Sony are very comfortable in the very beginning, but then the pads start getting a bit tight and uncomfortable. Sony still seem comfortable enough if you take them off for a few moments every now and again. They are incredibly light compared to T1s. I like the headband regulation on Sonys more as it is more precise and much less prone to sliding on its own.
MDR-SA5000
Stage right next to the listener, a small studio and not a huge club. More intimate. A tiny bit brighter and thus seem more transparent. Might get a bit fatiguing during long listening sessions.
Bass is there when called for, maybe 10-15% less than one might want, but also not as controlled as on T1s. Overall, not as balanced as T1s, but still excellent.
They remind me of T5ps - I loved them and think if someone needed a cheaper, much better version of them SA5000s might be what they are looking for. Brightish, bass-lightish, but paired with a good amp will totally shine.
T1:
Stage a bit farther away, female voice a bit less in the centre of the image. Everyhing spaced out better, better defined soundstage. Not as bright and seem a tiny bit less transparent because of that. Completely fatigue-free. More balanced and suite for more kinds of music. Total all-rounders.
Conclusion
The main differences are the little touch of brightness in case of SA5000s (nothing excessive IMO) and more bass on T1s showing just how balanced T1s are. Looking at the price difference however, I
think SA5000s are a great value for money and pairing them with the right amp will make them shine and for some types of music (Classical and some synthpop) I would even say I would prefer the Sonys over Beyers.
Real world conclusion - if I were not crazy and did not want to spend $1000 on a pair of these Beyers I would buy the Sonys any day and never look back.
Disclaimer - I am not very experienced in looking for nuances in sound and someone with more knowledge would probably be able to describe them in more depth, but I have done my best to quickly show what my personal feeling about these two headphones are. Just my personal opinion and how I hear things. YMMV.