For balls out accuracy I would go with the Ferret. There's a thread in the precision rifles forum, sub forum .50 precision rifles about one person's dealing with Dave.

Read it first and then do your homework, talk to Dave and make any and all plans that you think you might need to.

Mark Serbu is a good guy, his shop is small enough that if you call at the right time he might answer. He'll tell you everything that you need to know about his rifles. He's also a perfectionist, so you know that whatever you buy it's gonna be good.

Safety Harbor uppers are good to go, search MrBen here on the forum. He posted a range report on his upper. They're tough as nails, his got blown off the bench from the muzzle blast of his BFG. Picked it up, loaded a round and smacked the 400 yard target!

Pretty much all of them are good to go, just have to decide how much you want to spend.