Alright... my first binder came in today. I have to say, I give a nice thumbs up to the US Postal Serivce; it only took two days to get here. Much faster than UPS and FedEx traveling the same distance for other things I've purchased.
I am going to put my measurements here just in case there's anyone out there of roughly the same size, that way they'll know about how well the 988 will fit them if they ever want to order it. My waist (measuring about 1 inch above my navel is only 25.5 or 26 inches) and the average of my ribcage and the biggest part of my chest is 32.5 or 32.75 inches.
With only a regular bra and tank top this is what my chest looks like:


I've seen pictures/videos of other guys with big chest, but I find that if they have kind of a bigger stomach, it seems like their chest can kind of be hidden more with their stomach. My stomach is small, so I was figuring that if I didn't get too flat, I'd just look like I have some sort of a giant tumor on my chest.
With my chest average of 32.5 or 32.75, Underworks sizing charts said I should get a small, so that's what I ordered, and this is what it looks like:


It looked promising, not completely flat, but it seemed fine, but then I put a t-shirt on and now I am disappointed:

It just looks like I am wearing a sports bra. It looks a little better with a button-up shirt over it:

But yeah... not too impressed. I think I'll get an extra-small next time I order, because the small doesn't feel tight, it wasn't even hard to put on, and it feels like things move around in there too easily. I am not going to return this one, because I think it's probably a good idea to keep one around that isn't too tight just in case I ever want to do an activity where I need a breath.
It doesn't compress too much on the top, so I am getting this weird cleavage thing as it I was wearing a push-up bra. I can tell the shirt was made for people with bigger shoulders, because it seems to hang too low on me. I am going to do some alterations on this shirt to see if I shorten the shoulder straps (I think I can take about 3 inches off the shoulders) if it'll fit better. I think that will fix the cleavage problem and make it look more flat, because it will raise the compression material up more.
So, if you're about the same size as me, just go with an extra-small.