BB yep Roy is right. The single TO4z i had was a heck of a lot better from a response and outright power persepective than the T78 i had before. However compared to the twin -5's I have now they are better still. A lot less doughy low to mid compared to the TO4z and so i get much better average power which is what i want on the circuit. I gave Roy a drive with the single TO4z just so that he could feel first hand the dullness in the low to mid range that i was telling him about b/c he thought that it really shouldn't be that unresponsive down low going from all the talk on the net and dyno graphs of other single T04z's etc
Don't get me wrong I'm not saying the TO4z is a bad turbo, it's not, it just didn't suit my purposes......if i had 3ltrs though I would have stayed with the single
If your intention is for a responsive ~350rwkw then I would recommend sticking to twins -5's.
URAS, the -5's you mentioned would be one of the turbo's i imagine JAGR33 would name They have pushed over 360rwkw on a number of standard stroke gtr's not to mention 400rwkw+ on an rb29