especially with SD, i doubt you would notice any difference, when you get your heads done or aftermarkets, get a set of 1.7 rr's in there and some stiff valve springs
i agree with dbeck, if you're still running the stock rear end gears, swap those out for some serious difference
i dont think RRs are a waste for stock heads, they are reusable and dont wear and can go from one motor to the next, think of it as setting yourself up.
they're moving up and down at exactly 1/2 the speed of the motor, and moving that often for a long time, somethings going to wear, but you're right they can be swapped motor to motor and for the most part would still be good for a while
but i could also get a huge x cam for when i get a 383 in 10 years, that way i can just change it over when i get that
wont give the best performance until then though, and wouldn't be worth the money until other mods arise