My thought was price/ availability and age. The Rx8 box sits around the $500 mark second hand, where as the T5 that I had come across where around $1000 plus and many years old. The thing i dont like about the Rx8 box is the factory starter hole, as its actually on the bell housing,although the adapter can be made to cover that. As i havent bought either yet I would happily look at either again.
My thought with the 3.0l V6 was that it could be still said its a 3.0l V6 capri
and also already being a rear wheel drive motor. It seems potentially allot of money can be consumed in a front to rear wheel drive conversion.
Additionally, based on the Code of Practice for which Qld approves mod plats, engine capacity is limited based on kerb weight, particularly if wanting to add a turbo at a later stage. The 3.0L is still a suitable size that could be turbo'd later down the track, if desired.
Its great getting peoples thoughts as it challenges my thinking and whether I am heading in the right direction.