046 full of fuel and oil 20" bar 76.5cc.. Feels really nimble and def not rough on the ol back or arms all day. But for a super lightweight all arounder id recommend a 346xp or 026/260/261.Not sure about auto tune but I think that's Husqvarna . Stihl has the Mtronic. Auto adjusting for conditions. Altitude, humidity, temperature and even less than clean air filter. I've been running 3 stihls with no problems so far. The oldest one is over 2 years old and the newest about 4 months. You mentioned an 18# 70 cc saw,my 462 is 13 lbs, powerhead only.
EDIT. Stihl has come out with a fuel injected saw but not available in th US yet. 500i,80 cc