One of the first things I noticed in-game is the valve float of pushrod engines and, while your basic pushrod small-block V8 starts to see valve float around 5000rpm IRL, there are a host of things a manufacturer can do to improve them. All add cost, but do wonders for reliability, especially when comparing a geared pushrod cam configuration to a belt-driven OHC.
As you push the quality slider, flat tappet lifters give way to rollers, rocker arms follow suit. Rollers can withstand a much higher valve spring rate and, since they are so much more resilient, can be engineered for higher rocker arm ratios, which translates to higher lift. The result is a 7000-rpm screamer with a respectable idle.
This also gives rise to some extra valvetrain components--tradeoffs between reliability and performance. In the "reliability" column are things like double-roller timing chains and timing gears, roller lifters, heavier pushrods, a lower rocker-arm ratio, and less valve lift--less force on valvetrain components and a positive valve to piston clearance.
On the performance side are lighter pushrods, aggressive rockers, heavy valve springs, oversize valves, maybe some warped valve seats, and, of course, negative piston-valve clearance--great for performance until something breaks. If you are really lucky, you'll only bend 1/4 of your pushrods and your valves will still seat. Probably not.