1) I have done London-Tehran all in sleeper first a few years back and I enjoyed the trip thoroughly.

London- Brussels-Cologne-Vienna- Budapest-Bucharest- Istanbul-Ankara-Erzerum - Tehran (erzerum- tehran was by bus, but there is a direct istanbul-tehran twice a week).

I stopped in cologne, budapest, bucharest, istanbul and Ankara.

2) 45-hour Beijing-Lhasa....beautiful scenery. A bit cowded and Absolutely horrendous restrooms though, but the trip is magical.