I'm a happy Zetec owner. Changed when the old xflow needed a rebuild, and decided it was the way forward. Although it is a heavier engine its still lighter than the Vauxhall lump (isn't everything ).
It retains much of the character of the xflow - when run on carbs, but because it hasan ECU and 3d mapping its far more economical (about 20% improvement).
The Ital axle can be a problem in the higher tuned Zetecs, but a "standard" unit should be within the capabilities of the axle. An upgrade to consider is to change it for a Ford unit at a later date.
You do need to consider if you will keep the car long term, upgrading as want/need/finances permit, or will you trade in/up. If the latter, you need to keep a close eye on what is selling well, for the former, remember, most bits on a Seven can be changed (for a price & some work) so find one you like
The advice I give people is to get down to a local meeting and talk to every owner you can, and get your bum on as many seats as possible.
Dave H