BEC's.....
 

.....which one basically?

Never had to use one before so no clue on them at all. :)

I'm using a Castle Creations BEC Pro, but that's just so I can output at 9.6V...

I'd always recommend the Castle stuff, though Flightpower will probably do a good BEC too. The standard Castle BEC would be enough for your set-up (easily!), and it's not too pricy either.

I just used one of these tel: A 5/6v 3-5A UBEC
just from ebay.
Dont need one on the bigger dedicated speedos though

Is it capable of running 16.8V input though?

it was for 14.8 on my application, i didnt see tels system?

James, you have PM dude!. :)

i use the hobbycity ubec 5s lipo max 5-6V to receiver works great in a 1/8 scale truggy, also with the hobbywing ez-Run 150esc i don't use a ubec cose there is allready a good one in the esc and i also don't use a fan on this esc on 6s lipo with a 1600kv motor.