It's been more than a year since I started this topic. Short recap: back then my Das with MX Blues was destroyed and I tried switching to IBM Model M. It didn't go well -- my fingers were extremely painful after few minutes of typing. Then I posted here looking for advice. Pain didn't go away (in fact, it took 4 months for pain to subdue!), and I bought Filco Majestouch-2 TKL with MX Blue switches. That made my life better. In the year since, I found out that I suffer from RSI (Cubital Tunnel Syndrome, on both hands).
A month ago I bought a nice IBM Model M terminal keyboard with 122 keys (very cool German layout with German legends on some keys! -- I'll post that in separate topic) for $30. I didn't plan to use it, but it was so cool that I bought it. As I bought it during work break, I brought to the office, and left it there. Two weeks later, RJ45 to USB Soarer's Converter came through mail, and I had a chance to try out the keyboard. Now, short explanation. At home, I have a very nice low office desk, which I always considered to be very ergonomic (it's low, so wrists are in pretty natural posture) -- and that's where I tried to use Model M last year. At work I have a special ergonomic keyboard tray - it's fully adjustable so I adjusted it to be even lower (it's touching my lap) and to have as much downward slope as it is possible. And when I tried that monstruos terminal Model M on
that desk... the angels sang

So it seems that for the whole time, problem was in those few degrees of the keyboard's angle (I'm sure the difference is 5 degrees at most). I still feel tiredness in fingers after typing on Model M, but almost no pain - and that's compared to MX Blues which were my favorite painless switch.
Typing on IBM Model M is the best thing that ever happened to my fingers! OK, to be honest, that terminal keyboard is not very usable (an inch too wide for my keyboard tray, so I can't push the tray under the table), and my old Model M is also not very usable (3 dead keys since last year when everything worked OK, not sure what happened), but buckling springs are the best switches ever! I plan to buy Unicomp EnduraPro in beige, as soon as they'll have one in stock (I like the trackpoint -- even if it's not very good, it will still give me freedom from mouse and my RSI-suffering hands will be grateful).
I'd like to thank all of you who in May 2015 tried to persuade me not to give up from Model M. You didn't succeed at the time, but occasionally I did think about it, in part because of your words of support
