yaar its upto u. If u are like racing etc, then obviously shift at max rpm. But during city drive, try to shift at 3000rpm or below. Even 4000rpm is too much.. And at low rpm u get better economy..
And about resale:
Kush keh nahin sakta, Agr engine achi condition mein lagwa lo to resale pr koi affect nahin parrna chahye itna ziada, mugr agr engine low condition mein lagwain gay to resale kam ho gi.
Aur head change karwaney sey resale tab kam ho gi jab koi bewakoof khareed raha ho to. Warna if the swap is successfull without any problems , then resale pr itna affect nahin parta.