Leaded or Unleaded?

Officially, all Saabs manufactured since 1985 are able to run on unleaded. Note, that some models had catalytic converters fitted prior to them becoming mandatory in the UK. If the vehicle has a catalytic converter you *must* use unleaded.
It may also be possible to run pre-1985 engines on unleaded.
/john

These are typical figures for a 175hp 9000 turbo (source Eric Dymock 50 years of Saab):
Max Speed 138 mph/222 kph
24.17 mph/38.8 kph @ 1,000 rpm
Acceleration 0-60 mph 8.3 secs
Standing Mile 15.9 secs
Average Fuel Consumption 22.7mpg

I think I would find the 9000i a "bit sluggish" but perhaps a service would help it - especially if you do not know the service history.

Use unleaded fuel in your 9000 (if you can find anywhere to buy it in the UK at the moment) http://news.bbc.co.uk/hi/english/uk/newsid_920000/920527.stm
/john

Will a 89/90 2.0 litre turbo Carlsson run on leaded?

NOT if it has a catalytic converter, no.