You can get either turbo with either cover (62mm and 67mm). Straight from the PTE turbo website:
62mm turbo:
• Compressor cover options:
- "E" compressor cover 3.0" inlet/2.0" outlet
- "Ported S" compressor cover 4.0" inlet/2.5" outlet
67mm turbo:
• Compressor cover options:
- "E" compressor cover 3.0" inlet/2.0" outlet
- "S" compressor cover 4.0" inlet/2.5" outlet
- "Ported S" compressor cover 4.0" inlet/2.5" outlet
- "H" compressor cover 4.0" inlet/3" outlet
- "Ported H" compressor cover 4.0" inlet/3" outlet
I have never heard of the "mid range" being an issue to be honest. I have also sold over 40 of these turbo kits with the smaller non ported compressor cove, and have never heard about any issues with compressor surge. The SP (S-ported) covers do flow 3-5% better, and according to the manufacturer this only comes to play above 32psi.
Here is a 350z Dyno with the 6266 turbo and the open inlet .81a/r (equal to a 1.15 a/r divided inlet) T4 turbo, with the E (smaller, non ported) compressor cover:
As you can see, there is no problems here with mid range power delivery. This was also the less efficient mid mount turbo kit, and not the twin scroll I have available for the 370z here.
Vince told me that there was another 20-30whp left in this setup, but since the customer wanted 600whp, the tune was left very conservative and as is. This tune was done on 93 pump gas.
Due to the 4" inlet on the SP cover, I am not able to use it with the twin scroll kit. There just isn't enough room for the air filter, and the piping to fit in such a small space.