I'm considering a Jive Pro 120+ HV ESC for my X7. The built in BEC is rated for 8A continuous and 20A peak. It also has two power leads. I'll also be running BK servos and an Optipower UltraGuard. Will this BEC sufficient to handle everything, include acro rescue? If not, what would be recommended?

From Kontronik manual :
For safety reasons, we recommend connecting either a 2-cell LiFePo battery (BEC voltage: 6,6 V – 7 V) or a 2-cell Li-Pol (BEC voltage: 8 V) or 4-cell Ni-XX (BEC voltage: 5,6V) in parallel to the receiver.

+1

I am using jives, helijives and jive pros on all my helicopters, When using the BEC in the ESC, I always use a buffer pack. No problems on any of mine, running a variety of brands of servos.

Using a buffer also means you'll always have cyclic and tail control if anything really bad happens (flight pack connector failure, among other things)

Yes, exactly. Same experience. I never had a problem with Jive BEC AND buffer pack.