Yellowstuff are very good on lighter cars (I've run them on the VXR and MR2 with success) but on heavier stuff they can give up quite easily.
If it were me, I'd change fluid and not just another lot of the RBF600. I ran the Endless fluid in my Zed which being a ragtop weighed a fair bit, and saw some horrendous temps on track but the fluid NEVER failed at all. It's ridiculously expensive, but then it's also utterly incredible so you do get what you pay for. I currently use the ATE 200 as well, which I run across the MR2 and the BMW, as well as the 911 before that. All have been tracked extensively, and I personally prefer it to the RBF600. It's not as good as the Endless stuff, but then it's 1/3 of the price.
30mins on track is excessive, both on the driver and the car unless it's specced for race stuff. If you're a heavy braker as well then that's equally not going to help. And turn the traction off!