Trend is toward stiffer pushrods ignoring weight there--I use titanium retainers on everything I can--over the years it has proven to be the easiest way to get better spring life, better rpm and more protection against loss of control--never race without them. On the dyno you find out pretty quick that engines love more spring pressure thus better control---big solids like the beloved .590 and Comp .650 always run better with more spring.
My Nascar pal tells me they turn 10K rpm now but the valvetrain is so very light they do it with 125 seat and 300 plus open so...weight is everything!
They are going roller next season so...I expect RPMs to climb up and up--I bet 11,000 is going to be the slow pokes and some will turn more--has to happen--it is the only logical place to find more HP.
Mopars have always had the heavy valves--11/32 " in all the aftermarket heads helps a lot but then when you get Indy and Hemi size heads it is still trouble--the best running race stuff alwyas has titanium valves--you can Hear the diff on the dyno--every time!!!
Average racer should not load the car on the trailer without titanium retainers in my book.
Taller springs, bigger diameter are always better.
Better control, better life, more RPM every time.
I have never been able to see a loss from mechanical --like more pressure etc---the gains from better control always trump the mechanical myth in my experience.