My bag now is a 15l and I didn't think the R20 (20l) would really cut it. The R25 also had two front buckles which to me would withstand a crash better than one. I keep my rain gear, work boots, extra visor and other misc. gear in the bag. It gets full and heavy quick. Plus, for me the $139 to $189 wasn't that big of a deal but it was harder for me to justify $239 for that HUGE R30.
Never Trade the Thrills of Living for the Security of Existence.