I found this chart on line:



My guess is that my R350 is a little bit stiffer than the newer R300. The 350 is made from 6AL/4V while the 300 is made from 3AL/2V. If I were buying a frame today I would go with the Helix to get the 61 cm top tube (I have ridden them since 1981) and to get the 6AL/4V material. But most people are not forced to lug around my 105 kg, and for those folks, the R300 might be just fine.