Lately i had chance to do WE2 with 4% fxo and 2% xrt.
Result - my xrt time was like 0.05s slower without any practice after few laps. fxo time was pretty decent.
Wallbrake? Pls... think noone is using it, atleast not me...
Slipstream? FXO with 4% cant do nothing with slipstream against xrt, similiar to xfg and xrg.