Don't know about the Extra channels as BT have never managed to get them working on my Youview box, [another reason to jump ship], but I do know that Catchup TV works the same as using iPlayer on a computer, you can watch it, pause it, but not record it, unlike the Sky Box which downloads them to your planner.
I got one hoping to leave Sky as well, for the same reason as the initial poster, I only record a few programs mainly on Sky 1, Fox and Syfy but have now decided to stay with Sky and use the YouView boxes for recording any of the 70 channels that clashes with the stuff I record off Sky.
I cancelled Sky Movies (£16) and now have Love Film & Netflix (£11) for films.
Bob WRBRIX
BT Infinity 2 - Fritz! 7390 ~ Sync 79.99/20 Mbits Actual 76.27/19.69 Mbits @ 320m
DialUp to CIX, BT Home Highway+CIX, ADSL1 Nildram, ADSL2 SKY & Be*Unlimited