With the same ship I decided to see how fast I could go, just reached 10,000km out at 44 minutes in and going at 4,350m/s decelerating at 0.30 m/s/s, I estimated just over 40 hours to lose all velocity assuming deceleration stays the same which I assume it won't. I think I might end the mission now and assume they are lost
( just ended the mission and the highest speed was 4860 on stock parts, my best yet )
Just before this one I managed to achieve a relatively stable orbit between 40k and 50k (until I went and watched TV for 20 minutes) with enough juice to bring her back down to earth this time, unfortunately I landed almost directly on the north pole (passed home base while watching TV) and the dark side bug blew up my ship
And here is Orbiter 2:
It consists of 6 central LRBs with 2 fuel tanks each in the centre which fire from the start, the lower SRBs fire at the start and can then be dropped after the first stage. I then wait until about 1/3rd of the fuel in the last LRB tank is left and fire the second set of SRBs as these must be dropped with the LRBs for now. I figure leaving them until the latest time is best as air resistance will be less and I might get more velocity from them.
Once those SRBs and LRBs are used I release them and fire the third and final set of SRBs which are attached to the primary LRB core. Once those SRBs are used up the ship is coasting up towards the 35-40k mark, on it's own I reckon it might hit 45k. If I want to go into orbit I point the ship just below the horizon and use 3 of the 5 LRB fuel tanks to convert vertical velocity into horizontal and aim for a 40k height and 2400m/s velocity. I'm then left with 2 full fuel tanks for tweaking and coming back to earth.
When I did the highest velocity and distance I just burned all the fuel as soon as the last SRBs had dropped.