I think we are all jumping ahead of ourselves here.
To avoid a repetition of your TS experience. How many miles has the V6 done, how old is it, has the cam belt been done in living memory, has the water pump ever been changed, what condition is the radiator in.
All the add on go faster gismos will really come into their own if the cam belt goes as you will then have to make the vroom vroom noises yourself....Not a good idea...
I happen to think the 3.0 should have been in the car from day one. The 2.5 is gutless in comparison..as are most 2.5 V6 engines. The 3.0 would have given brilliant mid range performance exactly where you need it. I don't think it would have affected the GTA which is far too specialist for most buyers.
My initial reaction here was to say the 2.5 isn't gutless, but after re reading your post I see what you are saying, the 2.5 is a fantastic engine, but I only see the 3.0 being the same, but more, and I have trawled flea bay a few times for 3.0 engines. To me the only way forward in tuning a 2.5, is to put in a 3.0 or a 3.2 (or a 3.7
) to get 10 bhp froma remap is not really worth the effort
, stick a bigger lump in and then induction exhaust Q2 and re map.
I think the 2.5 slotted in nicely above the 2.0 litre, it has more power and performance, and is 500cc bigger, 25% bigger, the 3.0 is 50% bigger, that leaves a big hole in the line up, and the 3.0 would have to have been more focused than the 2.5 due to its extra power, therefore being much closer to the GTA in all ways.
From a petrol head point of view my line up would have both 2.5 and 3.0 in it, with the GTA having the 3.7 autodelta engine
I will finish by saying that the star of the range is really the 1.6 ts, for such a small engine in a large car its figures are very good, to finish - If you have a 156 its got a good engine in it, and you should be happy ts or V6 or diesel, I'd happily own any of them