I use AVO COILOVERS on my cossie and have found AVO to be extrememly helpful, they told me the poundage of the springs without hesitation, I know a lot of people try to keep this to themselves.
Coilovers do generally have higher poundages but this is NOT NECESSARLY due to being more compressed, you can get lower poundages as well as well as a choice of lengths, they are higher because they have to arrest(stop) the same weight in a shorter distance.
The diametre is immaterial, and is more a consideration of unsprung weight and clearance issues.

tabetha