[Glimpse]

I believe they changed them after the early 02's. The single springs handle the over-revs better apparently.

Correct; the single springs are less likely to float at high rpm. From a theory standpoint, dual valve springs are better at high rpm because their design is less susceptible to float and the springs provide good harmonics cancellation (meaning the two spring design absorb vibrations better).

However, the new single spring design is superior to the old dual spring design due to advances in metallurgy and construction. Thus, they are less susceptible to float than the old dual springs.