Any 944 owners (or ex owners)

Belts IMO are not that pricey compared to what you'd pay on a modern car. The parts themselves cost a bit but changing them doesn't take too long (access is quite easy). But it's best if someone who knows what they're doing does them. I got EMC motorsport to do mine, where the cam timing was dialled in. The car certainly now does go like a train (enough to hold off a new Cupra R (not too bad for an old girl I guess) so I'm not sure about the 'too slow in N/A form (I wasn't expecting it to be massively fast though I guess). This setting up of the verniers can help as much as 15BHP, and it applies to all 944s, not just 16vs.

As for people saying they are slow, the 2.5s had a cam fitted on the throttle body so that you had to floor the car to make it shift. A throttle response cam normally gets around this issue, and is quite a cheap alteration to make.

Check for the clutch being changed. Up until the late S2s the previous cars had rubber centred clutches, which now have a tendancy to fail, causing a driveline shunt and shaking when engaging the clutch around town when the car is fully warm. A spring centred (or 'solid centre as sometimes called) clutch will resolve this.

Rust is something else to check for around the sills and the bottom of the front wings.

As for which model of 2.5 that depends. Earlier 2.5s are faster thanks to less weight, and are cheaper to buy. Furthermore, the suspension is alot cheaper too (try £15/side for a lower arm compared to £200 for one on a post '86 car. But they do have the square dash... If you don't mind the square dash or less aggressive bodywork, I'd also say to look out for a Porsche 924S Le Mans. Around as much power as a 2.5 944, but with coilover suspension, different brakes and suspension. They really can give a 944 a run for the money and at the moment are cheap (although a few pricey cars are now starting to crop up in the Le Mans format).

Besides the brakes and some engine parts, I didn't really see how a later 2.5 was much cheaper to run than an S2. At the end of the day, they're a £40k car from the yesterday and will still require a fair bit of upkeep. But buy wisely and it shouldn't sting you too much .