consider this:

It will take many, many years for a snake to get full grown. Even if you went big and got a female BCC, she's not going to be a 50lb snake overnight. That's going to take many years. You'll learn how to handle her as she grows. The same goes for all your other options.

Also, you might try to stop thinking in "feet". Taiwanese blue beauties hit the 9 foot mark on occasion, and have been documented at 11 foot. I believe these snakes weigh under 5lbs at that size.

The pic I posted is probably a snake just under 10 foot, just comparing the length to the guy holding her. I can't see the end of her tail however. I believe I've read that the snake in that pic weighs 30 kilos. That's something like 65lbs.

I mentioned my carpet python earlier. She'll likely hit at least 9 foot years down the road. I doubt she'll weigh much over 20lbs if she even hits THAT, but I'm no expert on carpet python adult weights.

Try looking at pictures of OLD "fully grown" (they are always growing of course) snakes of the types you're looking at. Nothing gives you a better idea of what you'll end up with 5-10 years down the road than looking at pictures of the snake being handled.