There are 38588 = exactly 50 keys and 58380 keys >= 50 (including the exactly 50 ones). Most of the exactly 50 ones are unspent coinbases that probably belong to satoshi.. so most likely less than the difference so <20k, imo. The sum of all keys >= 50 BTC is 10722974 BTC or 89.4% of all BTC that currently exist.