Generally I do prefer it that characters not die too often from 'minor' encounters like the Death Star stormtroopers, unless they've been foolish (picked a fight with the frost giants who just want money to let them pass) or the occasional unlucky cohort. The CR system is good for this - an encounter of EL equal party level should give a good fight without much risk of PC death, although there are flaws - some low CR beasts can easily kill a PC of equal level in 1 round of melee. For the climactic battle with the BBEG though, I'd expect EL to be at least +4 over party level - ie 50% chance to win, all else being equal. In Conan TB the climactic Battle of the Mounds battle looked to be at least +4 over the heroes' level, they won through clever tactics, luck, and a little divine intervention from Valeria. Likewise the X-wing attack on the Death Star at the end of SWIV. If it was easy, someone else would've done it already!