For heavy items I use parcel2Go, I've found it much cheaper and faster than parcel force and fully trackable.
I recently sent a very heavy set of books to the USA, the cheapest via parcel force was £79 without tracking and taking upto 28 days. Parcel2Go cost £57 fully trackable and they arrived there in 2 days.
I also use them when I send heavy UK parcels for the same reason.
If it was a one off item I probably wouldn't ship abroad due to the costs involved.