yes, avoid the 405. it does have major problems with being too sensitive.
405cx fine, 410 better.
runs with dogs, I'm also looking at 910, also running ultras.
managed 7.5 hour 35 miler with the 405cx though. and you can also connect a little battery pack, garmin will still record but charge.
910 does look nice. no pace alerts still though, unless programmed.
my old 201 does it just in the menus, high & low speed to beep at. 305 too as well.