For $50K account, what is the interest rate your FCM/broker paid you? Please also post the name of your FCM/broker.
For $50k account with cash, IB currently effectively pays {4.28%x[(50k-10k)/50k]}= ~3.42%. individuals.interactivebrokers.com/en/accounts/fees/interest.php?ib_entity=llc. Just2trade, for example, can pay ~4.49%.
Oanda: 4.4%, since Nov. 1 Sep. 19 - Nov. 1: 4.65% Jan. 31 - Sep. 19: 4.925% Jul. 3, 2006 - Jan. 31: 4.825%, etc. Balance is not a factor. Current and historical interest rates: https://fx1.oanda.com/user/interestrate.html
Just2Trade They sweep funds into this http://www.reservefunds.com/ReserveOnline/RSVYieldsHTML?info=yields
mbtrading sweep funds to http://www.mbtrading.com/intRates.asp I choose Reich & Tang 4.34% independent of balance, with 0 withholding for non-US citizens. the yield might not have been updated for the fed cuts even though they claim it was