Well if you get the sport edition of the H&R springs... the ride is stiff... but not really really stiff... increase in feeling... and a little lower stance.... as for the bilsteins... just the regular sport shock they sell...
www.turnermotorsports.com sells this combo in a package... meaning the H&R and Bilsteins together... its a good set up... about 800 or so bucks.. but well worth it.. the Bilsteins have a lifetime warranty... and the H&R springs are made for your BMW... not just canned from another make... and model... and they are made in Germany... good stuff... I would put this to a "highly recominded" set up for the average sprinted normal road driver.
Now if you want the added stiffness and maybe a few times a month on a track.. and can deal with the bumps around town.. the track version of the H&R springs are just a bit stiffer.... thats about it.
Good Luck,
Les