Oh,my new name..!

You will find a lot of photographers use the EF500 with the 1x4....700mm@f5.6...cant be bad :-)  I take mine on and off the 500 accordingly!
Also, a cheaper alternative is to buy the EF300 f4 prime and use the 1x4...420@f4!
which I also use, or just the 300 by itself!