SWW - how thick is the rear ARB on your D5? I've got a C30 D2 and the rear bar is 19mm. I'd expect it to be bigger on a D5, but maybe not?
Looked at the Hardrace and I too thought it looked a bargain. However, I saw that it is HOLLOW, not solid steel like all the others - "Hollow internal structure". I'm no engineer, but I can't see how a hollow bar can provide as much torsional stiffness as a solid one of the same diameter. Engineers, please comment.
All that follows assumes you have as standard a solid 19mm OE bar.
If you go to 22mm solid it will provide an increase in stiffness of 80%. Not sure how much stiffer a hollow 22mm would be than a 19mm solid? How much increased stiffness are you getting? So it may not be the bargain it seems.
Going 24mm is 155% stiffer. The Elevate is 25.4mm, bit of a beast, 200%ish stiffer. That size will wind out a lot of understeer (turn-in will be epic!). But you may, unless you are careful, get oversteer, particularily lift-off oversteer - so the back could let go on you.
The Whitelines are reasonable, about £170. The 22mm BMR78Z:
http://www.whiteline.com.au/product_...BMR78Z&sq=5363
The 24mm BMR78XZ:
http://www.whiteline.com.au/product_...MR78XZ&sq=5364
If you have a look at these links and click the %Chart you will see where my numbers come from.
I know it doesn't mention our Volvos, but should fit your car. They confirmed to me by email that they'd fit my C30.