Gday 400TT,
I think its hard to make direct comparisons between spring rates, becuase of the different suspension geometry. You need to consider shock mounting points, angles and leverage, length of arms etc. In the CR a lot of the extra weight is in the AU rear end suspension arms as well (im guessing - as they weigh a ton), and this is actually "unsprung weight" as well.... so basically theres a lot of things to consider.
Cobra.AU, Through a hilarious set of circumsances (just ask me) I have some spare springs (maybe 2 lots of spares). 2 x 10" 400 (going on my rear) a 2 x 10" 425 (going on my front). I think I really stuffed up as I think I need 200's with a keeper (as Phil said), but Ill see how I go with ride height once I get it going (might be OK, as my shocks are a touch longer).
Your welcome to try them out if you like. They are QA1, and have an ID of 63mm through, whereas the avos standard is 65mm so not sure if they'll fit.
Cheers