You cannot generalize about single and double conversion. To simplify a
bit, the designer selects the IF as a trade off between image rejection and
selectivity. On double coversion sets the first wider IF provides the
required image rejection while the lower frequency 2nd IF provides improved
selectivity. However, you can also achieve improved selectivity with the
crystal filter. Since the SX110 has a crystal filter, the relevent question
is how effective is that filter.