How long does it take to call reactives and access reactiveValues?

library(shiny)
# Reactives with no changes (after first)
v <- reactiveValues(x = 0)
r0 <- reactive(1)           # 0 levels of dependence
r1 <- reactive(v$x)         # 1 level
r2 <- reactive(r1())        # 2 levels


# Reactives with change
vc <- reactiveValues(x = 0)
rc1 <- reactive(vc$x)
f_rc1 <- function() {
  vc$x <- vc$x + 1
  rc1()
}
rc2 <- reactive(rc1())
f_rc2 <- function() {
  vc$x <- vc$x + 1
  rc2()
}

library(microbenchmark)
isolate(microbenchmark(
  v$x,               # Use reactive value directly
  r0(),              # reactive with 0 levels
  r1(),              # reactive with 1 level
  r2(),              # reactive with 2 levels
  vc$x <- vc$x + 1,  # Change reactive value
  f_rc1(),           # Change reactive value, then call a dependent reactive (1 level)
  f_rc2()            # Change reactive value, then call a dependent reactive (2 levels)
))
## Unit: microseconds
##              expr      min        lq    median        uq       max neval
##               v$x  147.579  155.7295  161.7945  171.0895  1543.066   100
##              r0()  313.085  336.3540  350.3150  391.8150  2690.881   100
##              r1()  313.028  327.2900  343.7225  364.4280  1797.432   100
##              r2()  315.150  335.6495  349.1265  375.7345  4704.337   100
##  vc$x <- vc$x + 1  332.735  399.1075  684.4725 1142.8200  2653.368   100
##           f_rc1() 2223.533 2523.4550 2929.7770 3378.7445  5135.573   100
##           f_rc2() 3809.190 4202.9795 4632.9100 5245.2045 44846.423   100

Appendix

sessionInfo()
## R version 3.1.1 (2014-07-10)
## Platform: x86_64-apple-darwin13.1.0 (64-bit)
## 
## locale:
## [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
## [1] microbenchmark_1.3-0 shiny_0.10.1.9004   
## 
## loaded via a namespace (and not attached):
##  [1] bitops_1.0-6     caTools_1.17     digest_0.6.4     evaluate_0.5.5  
##  [5] formatR_1.0      htmltools_0.2.6  httpuv_1.3.0     knitr_1.6.12    
##  [9] Rcpp_0.11.2      RJSONIO_1.3-0    rmarkdown_0.2.54 stringr_0.6.2   
## [13] tools_3.1.1      xtable_1.7-3     yaml_2.1.13