So I changed out the original front pads with Hawk HPS @ 56,000 miles. They were toast with wear indicators chirping constantly. I just changed out the original rears @ 87,000 miles and they still had at least 80% left on them. Does this seem normal? I know the fronts do most of the work but the backs looked practically like new.

04 6MT
A few auto-x events
daily driver

i dont think it is normal, with 87k miles and it still has 80% life of the brake pad.
my rears seems to wear out faster than the fronts.

Seems strange. My rear pads and rotors on my 04 are pretty much goners and I'm at 34k miles. My carn's a daily driver, pretty much 100% city. My front rotors and pads got replaced twice under warranty due to the whole brake squeal incident when the 04s first came out, so they're still going strong.

/\ That also seems pretty early to me. With track days/autocross thrown into the mix, I could understand substantially shorter life if you use the same pads while daily driving.

my fronts wear way faster than the rears. i wouldn't worry about it.

Some of the variability in rear pad wear rates described above might be due to the effects of traction control/DSC on the pads. If you drive such that you are frequently activating the traction control and/or the DSC that may accelerate the rear pad wear. I remember a guy with a big mustang that forgot to turn off his traction control and set fire to the rear brake pads.