Hello,
I have lower spec brakes also.
With EBC yellow-stuff front and rear pads, whole track event in hot summer day wasn't a problem.
But I have good, cheep and effective cooling aids there

.
Actually I've prepared to upgrade to the upper spec because the front caliper difference is only its bracket (the thing between knuckle and caliper). But current setup is so well with 205/55R16 BS RE01R so I've postponed at least until front discs broken.
@
troek may want to know about the bracket. Just try to get second hand Legacy/Forester calipers with discs. It will just fit.
Regards,
Hanjo