I don't know about the very high ranks, but I can say as a level 30 armourer, using a level 35 leves and an engineer's manual gives me just over 1,000 sp per synth on some leves and just over 900 sp per synth on other level 35 leves. Bonus of around 1,500sp... I think! Not sure on that one. But getting 1k per synth with 6 sets of mats with the 900sp per synth with 7 & 5 sets of mats... lets just say the movement from level 30 armourer to leve 31 armourer was pretty quick. Engineer's Manuals are definitely worth it, and the leves are definitely worth it.