Hey there,
So you experienced understeer on the stock shocks?
Your assumption is correct; stiffer rear contributes to oversteer. Once you get your yellows on I'm sure your car will handle much differently. Full stiff is likely to cause damage to the shock; I ran 1.5 turns in front and 1.75 turns in the rear on my yellows (on GC's) and I was oversteering on the entry of turns quite a bit.
Putting the front sway back on will increase understeer; but I think you should drive with the yellows on and see how your car handles from there. Changing out the springs would be my next guess (lots of guys run custom Eibach rates via Ground Control)
Shingo