The GM based Saab engine is a straightforward replacement for the Vauxhall turbo.
It is common practise (or not uncommon in the UK at any rate?) to use the Saab engine in Astra turbos.
The Saab block is preferred because it is stronger, same for the other components too.
Alas Saab donors are no longer cheap as a consequence of so many being used this way.
In answer to your question, something that lasts.
You need to watch which Saab engine you go for, the later 9-3 aren't so good for this (not as strong) as the earlier version.
Last year I spoke at length to someone locally about they conversions he had done (/was doing), he uses a different ECU
if possible, favouring an Emerald unit.
Being a big fan of the Vauxhall motor and the Cavalier in particular, I am quite familiar with the popularity of transplanting a Saab motor into a Vauxhall. The Cav swap is most popular since the 9-3 shares a floorpan with it, making it virtually a bolt in job. And I completely agree, the Saab motor is MUCH tougher than the Vauxhall, with over 400BHP obtainable without significant bottom end improvement. Logistically though, it only works with a swap into another FWD car, the Saab engine has no mount points suitable for use in a RWD application whereas the Vauxhall engine from the Astra Turbo uses what is basically a generic "Ecotec" block which, because of it's use in the Omega, has the facility to be mounted in the longitudinal manner needed for a Dolomite transplant. I was always one for the KISS principal! And TBH, whilst the possibilty of a reliable 400 horses is an intrigueing thought, in practice, it would probably mean a much stronger gearbox, axle, suspension, and, probably, a tougher shell too, not to mention that 400 in 760kg of Toledo would make an undriveable monster! Yes I kinow that MOST Saab turbo donors are "only" SE spec 150bhp (as is the one I have) but 205 is factory Aero spec easily obtainable by map and a different turbo and injectors and higher outputs are similarly easy to achieve, it'd be rude not to!
Also, since I have already converted the Carledo to accept a basically similar Vauxhall engine, the Astra Turbo would now be a more or less bolt in swap, needing only the loom, ECU and downpipe to be changed, a couple of parts swapped on from the "original" Carlton engine and the addition of an intercooler. 200 or so horses will, I think, be plenty! And since all those Ecotec turbos are being pulled out of Vauxhalls to make way for Saab units, they are cheap as chips! (The entire 2003 Astra Turbo convertible I missed out on was only £800)