The t4 exhaust wheel is also a lot bigger than needed for the compressor wheels capabilities, so could be made better
Thats one of the reasons for the GT series AFAIK, to tackle the mismatch in the context of what people are doing now with a T4 (was designed for trucks originally IIRC, lol) although possibly they have gone too far for your specific applications, they are really suited to engines that rev better than most YB's I believe (honda engines seem to be a match made in heaven for the GT for example), but thats a whole other discussion.