Open loop is the best way to go if You don't use catalic convetrer. CL is only to protect cat conv not to melt and work properly, all emission related. I run LT1 (92 and 95) OL, with ignition and VE finetuned (i'm MAF delete guy) i was able to get more MPG and power at the same time. CL is always targeting 14.7 AFR (except WOT situation) so you won't get bes overall performance and that limits MPG savings.

best regards