To close this chapter, I just ran about 50 FMJs and a magfull of JHPs (all I had left) testing the new 7rd mag, not a single hickup.
I also rented an LCR - have always been curious about revolvers, but never owned one, and never shot a snubbie.
I very quickly realized that this is probably not a great carry gun for me. Even thought the felt recoil with .38sp in LCR seemed actually milder than with .380 in LCP, somehow my shots were completely unpredictable. With LCP, I can quickly dump the entire mag at 15 ft into a typical silhouette target, even though the shots will be all over the map they would generally stay within target; and if I take just a little time to aim and use a two-hand stance, I can hit the bullseye repeatedly (although not with every round).
With LCR, I had no idea where my rounds were going at high rate of fire, and I could only hit the bullseye when taking deliberate aim and staging the trigger. And even then, it took a while. Probably the combination of goofy sights, a bit more deliberate trigger pull, and me not being familiar with it. But after shooting half a box of .380 out of LCR, and picking up the LCP, I felt relieved even despite more snappy recoil.
Also, 5 rds certainly felt very limiting. So I guess this answers that question. I am definitely looking forward to getting a revolver, but it won't be for carry. Right now, I feel like I've made the right choice.