ggplot2: how to manually adjust scale_area

I have made 2 bubble plots called beta and km. I would like to compare the plots side-by-side but the scale_area seem to be different which makes it difficult to visually compare 2 plots based on the size of the bubbles.

If you notice the legends on the plots below, the scales are different. I think it is because highest BiasAM value on the betaGSD5 dataset ~ 64 and kmGSD5 data =100.

How can I manually change the scale_area such that the betaPlot scale match the kmPlot scale?

Also is it possible to manually set the legend breaks? Instead of being automatically generated, can specify I the legend however I want like this? 0-10, 10-30, 30-50, 50-70, 70-100,

100

betaGSD5 data: https://dl.dropbox.com/u/63947093/betaGSD5.csv

kmGSD5 data: https://dl.dropbox.com/u/63947093/kmGSD5.csv

Here is beta plot code

betaPlot <- ggplot(betaGSD5, aes(N,PctCens,size=BiasAM,label=NULL)) +
  geom_point(colour="red", shape=16) +scale_area(to=c(1,10)) +
  xlab("Sample size") + ylab("Percent censored") +
  xlim(0,100)+ ylim(0,100) +
  theme_bw()+
  opts(
 #legend.position='none',
  panel.grid.minor = theme_blank(),
  panel.background = theme_blank(),
  axis.ticks = theme_blank(),
  axis.title.x=theme_text(face='bold',vjust=0.2, size =12), #size=15 #hjust:move     horizonal, vjust-move verticall
  axis.title.y=theme_text(face='bold',angle=90, vjust=0.2,size =12))
print(betaPlot)

KM plot

kmPlot <- ggplot(kmGSD5, aes(N,PctCens,size=NewBiasAMpct,label=NULL)) +
    geom_point(colour="red", shape=16) +scale_area(to=c(1,10)) +
    xlab("Sample size") + ylab("Percent censored") +
    xlim(0,100)+ ylim(0,100) +
    theme_bw()+
    opts(
      #legend.position='none',
     panel.grid.minor = theme_blank(),
     panel.background = theme_blank(),
     axis.ticks = theme_blank(),
     axis.title.x=theme_text(face='bold',vjust=0.2, size =12), #size=15 #hjust:move       horizonal, vjust-move verticall
     axis.title.y=theme_text(face='bold',angle=90, vjust=0.2,size =12))

 print(kmPlot)