Most T3's (there are various turbos out there referred to as T3) will be more laggy than a T2H but it will have potential for producing more power. A GT28R would be a good compromise on a tuned CA18ET I reckon
The T3 has a different manifold flange too and so will require modifications to the S12 manifold. On the plus side there are probably more turbo's out there using the T3 flange, as per the Ford Cosworth (Sierra/Saphire and Escort) and they can therefore often be a tad cheaper.