You might look at the 62/65-14 if your not planning on adding in some injectors. I'm running a 62/65-12 in my twin setup and it spools night and quick even with my box turned off.
Look into getting a 62/71-14. You can have it upgraded down the road when you get more fuel. A bigger turbo without enough fuel to light it is going to be laggy and might not spool at all causing turbo bark and poor drive ability. Maybe someone who has one will step in and let ya know how their truck is.
I had a DTech 62/65/12 for awhile and didn't much care for it, spool was fair but cooling wasn't a significant improvement over stock. It was fairly cheap but kinda got what I was paying for. You might be better off getting a box stock S300 from somewhere else.