Hi mate
Do a search for tuning the 16V. I used to have a tuned 16V (head, cams etc) and to be honest my totally standard Williams is a fair bit quicker. The thing about tuning a 16V is that you only really make power gains in the legendary 4,500+ power band. If you looked at a RR graph for my old 16V, the difference over a standard 16V was that it made more power at about 6500rpm and the torque curve flatened out after 5000rpm (instead of tailing off).
The Willy engine was designed from the outset to improve low-down torque and gets 85% at 2500rpm. Thats torquey! To be fair, the 16V is a fairly torquey motor with a nice plateau at 2-3,000rpm - but it falls again until the power band. The Willy makes 100% torque all the way from 4000rpm to the redline as standard too.
What this means on the road is that the Willy is a fair bit quicker from A to B. If you dropped a cog at motorway speeds, then the Willy would only pass a Valver because of the extra power (which is supposedly 13bhp, but is usually more as 150bhp is quite conservative for a Willy F7R lump). But if you add some roundabouts and corners, the Willy will really show its teeth.
Add all this to the fact that finding and fitting a Willy (or early Megane Coupe 2.0) F7R bottom end is cheaper than most cam and head packages, and youll see why the Willy bottom end is such a popular route. Of course, you can tune the nuts off an F7P 1764cc 16V engine, but itll cost you! (someone here also argues that the 16V is better for extensive tuning, but I cant remember why and its not usual practice).
By all means buy a 16V, but as someone who once had a tuned 16V Id recommend 2.0 power for the average tuner.