[kenikh]

I had a very long phone conversation with Chris Carroll about this topic not too long ago. Conventional wisdom holds, but there is indeed some nuance with CIS.
The short story: 38mm and 40mm are a better choice than stock for all but stock motors.

Regarding my case, I was planning to stay stock, with some mild upgrades to maintain off idle performance. I was going with 98mm 8.5:1 JEs, and DC15 cams, maintain CIS via a Leask WUR. Chris said I was nuts, as with the upgrades I was planning, I’d be doing nothing but choking the motor.

I asked about 38mm I/E and he still felt 40mm I/E, and even 40I/38E, consistently performed better than 38mm I/E, given this spec. Shortly thereafter, I committed to a set of 3.2 Carrera HEs (38mm ID) as my exhaust. Although I wanted your headers, the slippery slope had already eviscerated my wallet and the $100 price tag was a compromise worth making. Otherwise, would have gone 40/40.

There's a MUCH longer story, but my fingers got tired while typing. If anyone cares, I might finish it - but there's a second level of depth around the fuelling resolution and control CIS provides.