Depends where you want to sell the gun. Don't use latin if you want to sell it in the US. It will go way over their heads.
Definitely don't use a name that's in, or has been in the game before, this rules out ones like 'Legend'
2 Sylables - no-one wants to use 3 or more to ID their gun.
Identify your customer first. Then think of a name that guy could respond positively to. Will you be selling them yourself or are the Planet lads selling them for you?
What sells the gun? Is it the personality behind the gun, and the asociation the buyer gets to that personality? is it the promise of extra performance, the look? Whichever one you pick will again lead you closer to the name.
Prego means 'You're welcome' in, like, italian or something, so that might not be the best choice.
You could use some names from your career maybe's - 'The Wrecker' has a decent ring to it?
Don't rush this though Pete, it's a really important decision. I've seen identically performing custom guns sell at vastly different rates, purely due to the name, and 'cool factor'.
If you do want to sell it in the states, you'll need a British name, something that makes them think they're getting something special from the country Ego's are made in, rather than the usual production stuff. The 'GBR' maybe. You could even use the London Underground sign in your marketing - the yanks will lap that **** up.
Give me a call if you want any help.