I have always thought "tight lash" cams were just another way to claim better numbers under the curve. Another cam sales device for sure! ( or every cam on the planet would be one!) I have seen race engines run and sound just fine but be much slower( several tenths) when lash was too tight--as in the valves never really close and "seal in" that lick. You have to get enough lash so that they really have a chance to close at the RPM you are racing at. I would bet my shop that on a dyno you would see very little diff going with more lash but too little can kill power. It is all bout RPM as well--a street engine is not the same as a unit buzzing 7500 RPM--Component weight plays even more as RPM goes up--Swapping to Titanium retainers can often make it feel like you changed engines in a drag car--If you were short on installed height like some small blocks even more so. It is a balancing act and lash plays a very small part as long as you have enough. There is no way to explain how much you can learn on a dyno in a year--it will dispell lots of BS "conventional wisdom" in a HURRY.
Light weight valvetrain GOOD, Belt Drives GOOD, stiff pushrods GOOD, enough spring pressure to control it all GOOD Chasing valve lash all over the place--a waste of time IMO. I have seen Bob Reed lash a Hemi in staging so fast it would make your head spin and he did NOT get them within a few thou--he lashed 'em and raced 'em--in other words--made darn sure it HAD some then went to it!!! Ya'll should to--and...in a drag engine do intake and Ex the same--it is EASIER and who thinks that in 6-10 seconds an ex valve will be hot enough to change the lash enough to make one millionth of a second diff?