Yeah WPC tends to have a bit more fat content in it, which is probably part of the reason it is slower to absorb than WPI (higher protein without as many carbs and fat).
As mentioned casein is a slow release protein that forms a curd in your stomach and releases small amounts of protein over roughly 7 hours. The lower levels of protein from casein will help prevent muscle catabolism (slow the loss of your existing muscles) but doesnt do much for building new muscle. Thats where you need a faster higher peak protein like WPC or WPI.
Generally WPI is best around workouts (before and after) when you want the fastest absorbing protein to get into your muscle quick. I'd use WPC if you were going to supplement with shakes throughout the rest of the day.
If you were going to add in casein as well, i would have it in the morning, and another one just before bed (half WPC/half caseinate). This is if you train in the afternoons.
Other things that can slow the gut transit time for WPC (so it doesnt go right through you), are fibrous vegetables like broccoli and green beans. Aside from anything these fibrous vegies take energy to process so can assist in weight loss to some degree.
Cheers,
H