GW-50156 and heart rate

Hey everyone, I'm new to the forum but I've lurked for a long time. I've tried researching my question but haven't gotten the answers I'm looking for.

I've been taking GW-50156 for a while now and have been loving the results. My biggest question is how does gw affect high intensity training endurance? I'm quite familiar with how gw works, causing your body to favor burning lipids instead of glucose/glycogen. This is great for marathon running, but how does this work for sprinting? I've done ketogenic diets in the past, and every time the one thing I notice is my raw speed slows down, probably because once I reach a high enough heart rate, my body can't burn fat fat enough to sustain the high intensity work.

How does this work with gw? It seems my sprinting performance has gone down dramatically, and I feel much more fatigued once the intensity reaches a certain point, yet I can run (slowly) forever. If gw causes your body to burn primarily lipids for energy, my body cannot burn fat fast enough to sustain high intensity training, right?

If I remember correctly once your body gets into that higher threshold of intensity it almost 100% requires glucose as a fuel source and if you're in ketosis there's only one place to get that and it's via gluconeogenesis from the amino acids in your muscle tissue and glycogen. When you're at lower respiratory rates your body has all the energy it needs because it only requires fat and considering your high fat diet combined with unlimited stores of fatty tissue it makes sense you can hang out in that range for much longer periods of time. Assuming you reach that upper threshold that requires glucose in the event you're completely depleted it would make sense you fatigue quicker because of lack of fuel source.

That's exactly the thinking I've understood. I'm just so confused as to why everyone recommends gw so highly to athletes that compete in CrossFit. I do not do solely CrossFit, in fact I mostly powerlift, do strongman style bodybuilding with a handful of CrossFit style true metcons per week. For example, today I did the workout Murph. Out of the 37 minutes I was doing the workout, I spent 13 minutes in my peak heart rate zone. I honestly spent just about the entire time in that zone literally feeling unbelievably fatigued. It makes me wonder if had I not been taking gw, my body could've actually used more glucose, therefore actually making me perform better. Any one else have any thoughts on that thinking?