Flies very stable and because the tanks are all relatively central to the mass, as it empties it remains stable which is damn important for a safe landing. Had many a space plane take off and make orbit nice and smooth but on the return cant fly straight at all because the center of mass has moved too much. Save the RCS for docking only since she doesn't hold much. I can dock it with only 3 units of rcs fuel if I nail the orbit interception to around 100m but has plenty for contingency.

The middle tank contains no oxidiser to save weight since you will be burning 80-90 units of liquid fuel to get to max altitude and speed and it saves about half a ton of dead weight. I chose a rocket tank rather than the jet one so when you refuel in space it still has a use as a regular tank.

Only non stock part is mech jeb which is ideal for handing air intakes so you can get the most out of the air breathers before having to switch

Flies up to 28km up doing a horizontal of 2000 m/s. Build up horizontal speed first before maxing altitude as horizontal speed affects air intake amount.. go slow at that height and you will starve the engines. I suggest flying vertical to 20km then a gradual progression from there until you reach the 28km celing and max velocity. Once this is achieved pull up about 10-15 degrees as horizontal speed will contributes to your climb at this speed anyway. Once the engines are below 25% due to oxygen deprivation (using prevent flame-out on mech jeb) flick over to closed cycle, currently set to hotkey "1" and climb to an apolapsis of 70km before cutting the throttle and just using light bursts to keep that at 70km as the thin atmosphere is still in effect. At 70km your horizontal should be fast enough that only a few seconds burn will circularise the orbit and you should still have enough fuel to pick your re-entry anywhere on the planet and land or arrange rendezvous with a station for a refuel.

SSTO - bullet