This is for anybody with older GPU cards. Bear in mind, the x17 work units can be ball-busters on older/slower GPU cards.
They're meant for fast GPUs. Some slower GPUs may still run them, but they'll take for-damned-ever and will return a lower amount of bonus points. If they run way too slowly, you'll miss the bonus points entirely and/or get so few of them for the amount of work your GPU had to do to get there, you might as well just go with the other WUs.
As with everything, "Your Mileage May Vary" definitely applies in this case.
For Khali, I see that your point-spread has changed since 9/12 when you changed your setting. It looks like you are trending 50K-60K every other day with 10K-20K on the in-betweener days, for an average of about 35k+ per 24 hours. The WU's are just too big for your hardware to get done in a single day, so you're spanning midnight. But overall, it does seem that your production has risen with the x17 cores and it may be worth it in your case.