I have tried with your suggested 60, using a different procedure to avoid not having enough horizontal speed in the end and losing more main engine fuel in trying to regain enough :
-full main engine
-taking off as soon as possible (usually 150/160 kmh) and gear up as soon as it can be pulled up.
-ascent angle 60 degree (attitude hold help)
-reaching 20 km altitude, drop the ascent angle to 5 degree
-when your projected trajectory will reach those 5 degree too, you'll be at +/- 35 km altitude
-wait until you're at +/- 1300 kmh (mach 4)
-open scram door and full scram engine
-lower main engine until being shutdown, do it progressively so you don't lose totally the "Acc Z" indicator (it should stay above the middle) and do not lose speed.
-at 60km altitude, increase your ascent angle to 12.5 , you should be by then at 4900 kmh (between mach 14 and 15)
-at 75km altitude, main engine max, then drop the scram and close scram door
-altitude 85 km , stop the main engine, go Prograde and wait until your at the Apr Node
-When you're at the Apr node, (always in Prograde) , full main engine again until you have built your orbit.
-Once you're satisfied with your orbit, stop main engine.
I have burned more scram than before, but the great benefit is that i am in low Earth orbit with more than 50% main engine fuel left !
Enough for doing lots of things and a re-entry.
I'm sure i can drop the scram earlier without losing anything, will have to experiment to see the optimal altitude in which losing the scram does not affect the trajectory in any ways.