Agree with all the above. the steel lines don't do much for the back. under hard braking (track conditions) Code says there is an average of 10 pounds of pressure on the rear tire, not enough to help you slow down. more likely to get the bike squirmy unless you are really good.
switching to a good fluid will make a world of diffference. On my R6 I had massive fade problems running fluid from autozone after putting on braided lines. Switched to race fluid (mail order) and things were much better, though on some tracks I would have loss of braking power near the end of the day. turns out the fluid was burning up. a quick bleed would get them back.
since them I switched to ATE Super Blue Racing Brake Fluid and the brakes are insane! After seating in a set of new pads I lofted the rear of the R6 at about 150 at the end of the back stretch of FUSA

. Hardly any brake loss through the day.
all this was done running DP HH+ pads. Next season I'm switching to Performance Friction Race pads, I heard they sell a set that is much more linear than the HH+ pads
hope that helps.