Also...how do they both compare to the Dahua Starlight turret?
Some specs below. The 3MP Hik is an Ultra-Low Light model, which is Hik's equivalent of Dahua's Starlight. So performance is about the same... it's just that for the extra MP you get, the image is virtually the same width as 2MP (128 pixels wider), it's just taller (456 pixels)... which isn't always helpful.
For the 5MP Hik, its minimum illumination is nowhere in the range of the Starlight/Ultra-Low Light models. IMO, if it's used in a low-light scenario, some tuning might yield OK static images, but any movement is almost guaranteed to be an unusable blurry mess.
Dahua HDW5231R-Z (2MP Starlight 5231 Varifocal Turret)
Resolution: 1920×1080
Min Illumination: 0.006Lux/F1.4 ( Color,1/3s,30IRE)
Hikvision DS-2CD2335FWD-I (3 MP Ultra-Low Light Network Turret Camera)
Resolution: 2048 × 1536
Min Illumination: Color: 0.005 lux @(F1.2, AGC ON),
Hikvision DS-2CD2355FWD-I (5 MP Network Turret Camera)
Resolution: 2560 × 1920
Min Illumination: Color: 0.01 lux @(F1.2, AGC ON),