Now, i'm not very good at explaining how to take down a 40, so you'll have to either watch me or find out for yourself. This is what i use on my exo fleet.
I use this experimental fleet setup to take out the fast ships, then take i out the battleships with my normal vega fleet, the best i've done is lose only 1 exo on the 40, but usually, i lose two. This is only until i get Talons/Night Hawks as i know that they'll be the new vega killers.
(Note: i use this fleet for more than just Vega killing)
Got any questions? feel free to ask and i'll try my best to answer them.
EDIT: Sorry about the extra photo, it didn't show up in the preview and i have no idea how to get rid of it. (EDIT: nvm, found out)