Test Driving a Pattern ! M5400

So sewers usually make muslins for patterns to check fit, but how often is function tested? That's what I'm trying to do at the moment.  I'm test-driving McCall's 5400, which has pattern options for various two piece swimsuits. 

I'm interested in making top C/D and bottom F.
So to test out the bottom I made a pair of underwear!  (The dreaded word).

Pattern: M5400, part F

Size:  This pattern put me in size 12 bottoms.  Excuse me, McCall? Stretch? Negative Ease?  Based on prior experience with Big Four patterns, the experience of others (my best friend), and the advice of a 10 year old I made a size 8.

Materials Used:  I used a rayon jersey from JoAnn's. It's not very stable but it is pretty.  For the waistband elastic I used 3/8" knit elastic and for the legs I used a 3/8"plummy thin picot edge obtained semi-locally.

Directions/Construction:  Well, I didn't look at the instructions, so sorry about that.  I can sew underwear without them.  Also I didn't used their crotch shield and made my own instead.  No rules for me!

Alterations:  The crotch is wide.  Reeeaaallly wide, at least on me.  I trimmed at least 3/8" off each side.  I probably could have taken more, but better safe than sorry.

Fit: I like them, I do. I think the bottom left picture on the pattern envelope shows how they fit the best. They do show some hip, but not an enormous amount.

Future Alterations:  I think when I make them for swimwear I will definitely take a small wedge out of the bottom of the back part. It may be the rayon, but with the way they currently fit, I can envision some serious sagging.  This may be remedied with using spandex, which has much firmer stretch.