my 8cm is 18psi at about 3850rpm so not that far off from yours.
my biggest thing is being outperformed by the vf and the money ive sank into this to get a little more performance without going wild. i just wanted a little more than the what the vf offered. nothmans dyno plot looks nice for a dd and wouldnt be outran by a vf car.
i would be happy if i was overlapping at 4k too. it should since im making 18psi there. would more timing help with that or hurt it? my car feels like the airboy shows. i like midrange power and that why i went with this turbo. i think i was running less timing with the vf, not sure though.