A little late to the party here but I did a peds residency followed by an anesthesia residency and am now doing academic generalist anesthesia. Pretty much everything everyone said here rings true, so I won't try to repeat too much. I will say that peds is just really awful from the standpoint of requiring a ton of extraneous and lengthy training. Don't even get me started on the hospitalist fellowship nonsense. I'm not sure why accredited peds fellowships are three years except to say that specialized cheap labor is awesome for hospitals.
I told myself I wanted to be the PICU/peds anesthesia rockstar towards the tail end of med school and got interested in that path after I had already applied to peds, so was too late to do the combined programs. I did genuinely enjoy my peds residency on the whole, but I will say that if you go into a combined program with the goal of being an acute care badass, you will absolutely detest and despise the outpatient component of your training which will be next to useless in the long run of what you want to do.
The longitudinal relationships and chance to watch pathophysiology and trauma evolve over time is what attracts me to PICU, and at the current salary I make as a generalist the financial opportunity cost for that training, with interest over 30 years or whatever my career will be, easily hits seven figures.
That may ultimately be worth it to me- money isn't everything, of course, but when I consider even doing a peds anesthesia and maybe even adult cardiac fellowship (I've come to think you'll never be the best anesthesiologist you can be without adult cardiac training, but that's another soap box) in two years vs the four it would take me to do the original path of PICU plus peds anesthesia, it just hits home how crazy long this training path actually is. Mad props to the Hopkins and CHOP allstars who did it (and who inspired me to do it), but you cannot comprehend now at the end of med school just how long and exhausting that is. You just can't.