Just an initial impression of these, having bought a pair in the sale last week;
I bought a pair of 777S-21od in in September last year and have got on with them very well - they have taken regular wear until recently to fully break-in and be properly comfortable diving around after kids and sitting at my desk (and I've no doubt they are only just getting into their stride).
I bought the SST in virtually the same dimensions (though as has been mentioned above, technically a size up on the OD's). Straight out of the (paper) bag these are equally as comfy and I'm enjoying the stretch. Contrary to what others have written about the denim I find the stretch really quite noticeable. That's maybe just the 777 cut and where I'm needing them to stretch, though.
Like-for-like, the SST seems to be easier to just get in, and go.
I'm no purist, so the 2% inclusion doesn't bother me at all and it seems to sit well with the IH approach. It'll be interesting to see how successful the SST is and if it makes it to other denims. That said, there's hopefully some XHS/UHR in my future somewhere too, though!