I've owned a 5 turbo for the last 10 years, as well as a 172 cup and I think I can answer this question for everyone.
A standard 5 is not fast, a 172/182 will leave it for dead...
The thing with the 5's is that you can wind the boost up quite easily and for not much money they will put out a reliable 170/180bhp, even as much as 200+ with the right things done to it.. at this kind of power it will either have the edge on a 172/182, or at 220bhp it will be leaving it no problem.
Finding good ones on the road are few and far between, there's a lot of bodged ones which have had cheap mods, too much boost, etc hence why they have a bad name in terms of reliability etc.. but in general if you do the right mods, stick within the limits (sensible boost), and look after them they are very very fun motors, more fun than the clio in my own opinion due to the fact they are so basic and raw, almost like a go-kart in terms of driving/handling...
On the other hand I would say that the 172/182 is far more refined and easier to drive, as well as a lot more reliable and takes far less maintenance!..
It's all down to personal choice really, but to say which is quicker, its not so straight forward because it all depends on the state of tune of the 5 you are racing, no two 5's are ever the same these days as 99% of the time they have been played with in terms of tuning.
If you check the link that Ashy posted, you can see the best ones are doing 11 and 12 second 1/4 mile times, which is much faster than any hot hatch you can buy out a showroom today...
http://g7wfs.sytes.net/cgi-bin/leader_board.cgi?engines=all&tyres=all