Standing with 20 will win at a higher percentage than splitting and doubling down, but your return on investment will be much lower in the long run, if i played it each way 100+ times my winnings would be even higher and keep getting higher the more times i played it out
I played this situation lot more than “100 times”. The average returns listed in my post above were taken from my simulator after running for 200 million hands. The average gain is ~0.7xBet if you stand and ~0.45xBet if you split. That is not 0.45xBet per split hand, that is 0.45x your original bet.
If the dealer shows a 6, a bust is by no means gauranteed. There is a ~42% chance of the dealer busting. If you doubt this, see the final dealer probabilities listed on Wizard of Odds at http://wizardofodds.com/blackjack/appendix2b.html . Note that 10% of the time that the dealer shows a 6, his final total will be 20; and 10% of the time the dealer’s final total will be 21. Yes, the 42% of the time win the dealer does not bust, you will win more than your original bet… the problem is the 58% of the time when the dealer does not bust.
PS — In an early post, you implied doubling immediately after splitting a pair of 10s. Note that this is not possible, as you do not have a chance to double until being dealt a second card in each hand. This could explain our different results.