Isabel was nice enough to track down these Land's End rain trenches for me, and they arrived today.  I have them in two sizes, small and medium.  Note that in these photos I'm wearing a thin, sleeveless dress under the coats.  Since this is going to be a spring/summer raincoat, I don't need to layer anything huge under it, but I might want to be able to wear a blazer or something under.  The weight is good and the fabric seems like it's pretty waterproof.  I'm unsure about the fit though; I suspect I may be between sizes.

1-5 is the Medium.  There is definitely room to layer anything I want under this, but I think it may look too big/sloppy overall, especially in the top/waist.
6-9 is the Small.  I think the fit on top is better but I'm not sure how much I could layer under.  (I will try later when it's cooled down a bit!  I nearly died of heat trying these on earlier...)  Note that the bottom button is unbuttoned in these photos as the hip is too tight when buttoned.  I may be able to move it over a little if I decide to keep this size.

#10 is my existing blue trench, which I still like but which is kind of useless as a raincoat as it has lost all semblance of water resistance. Size wise it is somewhere between the two Land's Ends coats, and there is a belt and flared bottom which helps a lot. 

So, what do you think?  Is it is a keeper?  What size?
ETA: another option that Parsley and others suggested would be to use waterproofing spray on the existing one (#10).