if your really that concerned about overheating, try slapping a couple of small radial single radiator panels to the parts that overheat first but install them in a way that they wont cause much drag also offset them more into the body of the craft to minimise drag again, youll get a bit more speed out of your airbreathers hopefully that way before your climb with rocket ignition, who knows ,might work, i can build space planes but nothing that reaches much further than the mun but these days i focus more on humongous, single shot and return rockets, capable of mass kerbal transit, i find the best way to get anything out far is to send it to duna first and use ike for slingshots
