no way i believe that a rear turbo set up is going to spool faster than a normal setup. the reason you "don't need an intercooler" is because the length of piping form the back has more volume (but much less surfce area) than an intercooler and the air coing by cools. so it is an intercooler of sorts that has not much restriction, but a lot of volume and ver poor cooling efficiency. your major lag is going to come because the amount of piping in the exhaust before the turbo is immense and in order to fill that, it is going to take a while. i see it as a decent solution when space really is an issue, but in 90% of the cases, it is a very poor soution.