Yes 500 is your best bet. If you go by the traditional bet your lead minus a chip you would bet as much as you could here and bet 1000. However a bet of 1000 would not protect you if BR2 wins a doubled bet and you lose your bet. By betting 500 you can lose your bet and BR2 can win his bet and you still win the session.
The cards are delt and the following is :
Player..........BankRoll............Bet.................Cards
BR2.............3000..................1000.............10 +10
You..............5525....................500................6+5
Dealer..............................................................5
BR2 now splits his 10's and gets 3 more 10's and splits to 3 hands with a 7 on the third hand. The situation is:
Player......BankRoll................Bet...................Cards
BR2a..........3000.................1000..................10+10...............Stands
BR2b....................................1000..................10+10..............Stands
BR2c....................................1000..................10+7................Stands......
You............5525...................500.....................6+5................Action?
Dealer................................................................5
What do you do now ?