Proton started with Proton-K (Proton-Zond) to Proton-M and has now grown to major phases 1-4 and enhanced Block-Dm and Briz-M.
What is the latest geostationary orbit (GSO) capacity? I could not find it anywhere. Will there be some more work done (before they are being gradually replaced by Angara A5), or is it that the old railroad has it limits?
Found Space Launch Report but it does not provide easy detail. RussianSpaceWeb.com is pretty close. And here.