Late response as I've been busy at work with a big contract whilst trying to redecorate my office at the same time. 9.30am till 11.30pm at night leaves little desire to browse PF!!
My post is based on my experiences of building and driving RS's over the last 12 years and I agree with Karlos completely.
First off, the CVH head.
Large heavy valves that can't dissipate heat quickly leading to premature valve head failure when used hard. The weight of such large valves require big springs to make sure they close properly, adding stress to the valve train. The heavy springs cause large amounts of pressure onto the cam lobes and rocker studs, leading to premature wear of the cam lobes, followers, and pulling out rocker studs from the soft alloy head.
The Zetec bottom end.
Long stroke with poor rod ratio making it produce decent low down torque, but hindering it's ability to rev as well as having a weak oil pump. It may have decent flow but if you suffer a set of cracked gears in the pump, it can wipe out your expensive engine. Luck of the draw whether it lasts or not. Thinner bore walls than the CVH. The rod ratio was revised on the black top making it better to rev.
The ZVH.
I've driven a few of varying spec, and every one irritated the shit out of me. Tons of torque all at once (with massive wheel spin, followed by a disintegrating gearbox) then nothing after 5.5k rpm. With a T34 they are marginally better but still fell flat on it's face. They just feel like they want to produce shit loads of power and then don't.
The CVH.
The bottom end is good although quite harsh and needs good balancing. Oil pump is ok although I have found that they can be a bit hit and miss as to producing oil pressure on older engines of seemingly good repute. Strong as an Ox with steel rods. Just lacking in capacity required to spool larger turbos.
A decent spec Zetec is a long way from a ZVH as is a decent spec CVH. I would ultimately like to combine a Zetec head onto a CVH bottom end but lack of front oil returns causes big issues.