Answer to original question - lower in summer (got rid of massive 23,000 BTUH window unit on main level, installed 30,000 BTUH minisplit) by about 30-40$ per month, which is about 15-20% of the bill. Used everyday for cooling. In the shoulder months, used for heating, in place of wood and some straight electric - little to no change in electric bill. May have had other use drop, however (daughters using hot water and electric, eg).
Things are ridiculously efficient.
NOTE ON OVERSIZING - Get a variable speed compressor unit (with inverter). They can operate at lower BTUH loads, so oversizing is a non-issue. My unit is a 30k BTUH unit, but can run as low as 10k BTUH, so there is not a risk of having clammy air because it cools too rapidly and leaves a cold, humid room. All automatic. Strong recommendation.