So I just got a nice 1st slot energy rune from Hell difficulty on the first boss. 5*, blue with 5% HP(and +3 SPD) as the extra stat thing. 3 upgrades and bam, 12% HP. Nice. 3 more and bam, 19% HP. Noice. 3 more and +263 HP. Not as nice, but still nice.
12th upgrade went 4% crit damage though...