I'll let Kmac or Hoov speak to the COD's SERC, but I know the Hummer's would often be "not great" at MGTW, in hot ambient conditions.. Definitely sub 200fpm. Now once you've burned off fuel or it was cool enough to make 5100 SHP (it derates based on EGT, which is largely driven by DA and Ambient Temp) it would climb 4-500 fpm at a "reasonable" fuel load, say 5-6k. I know I didn't like doing practice single engine in the pattern above 7-8k with a nugget in the left seat, because, while it could fly Ok in normal ambient conditions if you weren't a goon, most guys fresh out of the RAG, me included, flew like goons when SE.. Safe, but just not enough seat time in the Hummer to have a good feel for how to fly it SSE.