I have both a Day Sailer II and a Mariner. Both boats use the same boom, so the mainsail foot is not a problem. The DSII has 145sf of sail total, the Mariner has 185sf.
On the recently completed Texas 200, I sailed my Mariner. I carried on board my DSII sails as spares since my Mariner sails are about 40 years old. My sailmaker told me the Mariner sails still had plenty of life in them for cruising. I thought the DSII sails would be good to use if the wind was also higher than expected as they also have two sets of reef points (I had two sets of reef points added to the Mariner main). I also figured I could use the jib as a storm jib.
John