uprated springs on there own make a massive diffrent, the standard shocks will be fine.
35mm is best to have. any lower and you will have to buy an adjustable panhard rod, as lowering over 35mm chucks the rear axle out of line. as for stiffness all the lowering springs are about the same. it doesnt matter what make you buy, they all do the same job. i paid for a secondhand set of 35mm springs £30... just be carefull not to get ripped off.
george where abouts are you from anyway, you around my way?