I have installed OpenBSD before it had UEFI support, so I installed in Legacy Boot mode (I have UEFI capable laptop). I personally use Grub2 installed via debian live amd64 standard image.
I don't have Gnu/Linux installed. I only have bootloader from Debian. I have Windows 8.1 and OpenBSD amd64. # cat /mnt/ext2/grub/grub.cfg \ > | grep -v -e ^# -e ^[:space:]*$ GRUB_DEFAULT=0 GRUB_TIMEOUT=5 GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian` GRUB_CMDLINE_LINUX_DEFAULT="quiet" GRUB_CMDLINE_LINUX="" menuentry "Windows" --class os { set root=(hd0,2) chainloader (hd0,msdos2)+1 } menuentry "OpenBSD" { set root=(hd0,4) chainloader +1 } Grub2 is faster than Windows bootloader.