I presume bhyve emulates a serial device, has a limited buffer and can only work so fast before dropping characters....
Your best bet may be to use picocom or some such term emulator program with a builtin support for "file transfer" or can use an external program such as sz/rz which are designed to deal with lossy serial lines. Put your "paste" in a host file and xfer it. Alternately add another emulated net port and ssh in (if you are debugging networking, this may require some ingenuity!).
