I have this discussion quite a lot with customers looking for different turbos so understand where the fella is confused and understand what he is looking for. The question seems to be - if you already own a 420bhp .63 T34 car and fit a comparable EFR turbo in the hope of setting it also to 420bhp, will the car be faster?

As I'm lying in bed it's hard to show the difference visually without Dyno graphs but think of it this way.
A turbo just makes a small engine into a big one, and it does that with pressurised air, so the faster it delivers the air, the faster you get a bigger engine. At idle, the YB is a 2 litre. A good one, at 15psi is closer to a 4 litre. The faster you can get that 15psi, the quicker you have the 4 litre engine.

The EFR's SPOOL is better, so it will feed the engine with the boost faster than a T series. Also, the engines response time between you changing your foot from power fully off, to power fully on will be greatly reduced with a faster spooling turbo, so regardless of final power being the same, the EFR will deliver it sooner when asked as it can go from zero to say, 40psi faster than any T series.

Secondly, as spool is much improved, your torque band should move left as the engines getting bigger, faster, thus giving you more useable torque area UNDER THE GRAPH. As an example, the T34.63 tends to make peak boost on the Dyno, when floored at 2000rpm, by around 4000rpm. An EFR will deliver the same amount of air by around 3500rpm. This is because the EFR turbo requires less energy to rotate it so it rotates up to the required speed faster. for any engine driven in this lower engine speed area, the car WILL be faster than a comparable T series equipped car driven at the same speed in the same gear. IE: 70mph roll on in 5th gear side by side.

That's why folk are saying ignore drag strips, as that's about top end power and most turbos here will be equal, as BHP is BHP. Once your out of first gear, a drag car never sees low engine speeds or has worries about spool times as it's just wide open throttle and high revs all the way. That is NOT a test of a turbos responsiveness, it's only a test of is ability to flow air with its wastegate opening and open. A road car turbo test is all about what it does with the wastegate shut. Two very different metrics.