This board seems to like valuing miles at 2 cents per mile, so that's $6,400 worth of miles. $8k - $6.4k = $1,600.

$1,600 is 8 meals at many Michelin 2-3 star restaurants.
$1,600 can pay for 8 nights in (what I consider) a 4 star hotel.
$1,600 will buy you a really nice bed that you could sleep on for years.
$1,600 can buy you a fancy new laptop.

Would you trade any of those things for C?

For me, I'll generally only buy up to W class if it's less than $200 per ticket. I'll sometimes only buy up one leg if that leg's difference is much less. e.g. For a particularly itinerary I am looking at, S was the lowest available fare. SFO-TPE S to W is a $170 buy up each way, while SFO-HKG S to W is only a $50 buy up each way. If I were to do an open jaw like this, I'd only buy-up the SFO-HKG leg and forgo the SFO-TPE leg.