Well the "Leviathan of Dis" was found to be over a billion years old. So if we divide that by 50,000 we get 20,000. Since a reaper is created after each cycle that would mean there's at least 20,000 capital ship reapers. Since reaper destroyers are believed to be created from organics not used for the capital ship that doesn't include their numbers. Since they're used as escort ships and ground attack and they're considerably smaller there's probably more of them then capital ships. Also reaper minds are connected so communication is instantaneous. Under regular circumstances Halo wins because their weapons are far more powerful. Since OP equalized shields and firepower I think the reapers will win by sheer numbers unless the covenant has more ships than them.