I have used a Tornado on the T2 and its possibly one of the best aftermarket coils going,it would give you 2-3'' extra depth,many folks say it goes deeper but thats not for me too say,its a very popular coil here in the UK and many folks who put them on not only the T2 but other popular brand detectors never take them off again and usually then sell the stock coil.
For the last 12 months i have been using the next model up in the NEL range the Storm coil,and once again that is also another lovely coil its deeper,but for a general all round performance improvement the Tornado is the way forward.
Its not just better in say depth but also of course it cover more ground,pinpoints very well and target separation is 'very good,i also have the NEL Sharpshooter and the big fella the NEL Big coil,i dont have any business relationship with NEL,i am just a happy customer who has bought them with my own money and not gifted for a good biased review.