Depends on how low you want to go...
If you want to keep your tyres for longer than 20,000kms then you won't 'have' to change you shocks (although it probly wouldn't be a bad idea) - about king springs Low/FE2 height, SL
If you want to change your tyres because the inside edge is worn down to steel belts while the outside is still near new - anything from SSL/SSSL, and you 'should' change your shocks to shortened shocks if you go this low...
Rough idea for you, I'm sure they'll be other opinions
EDIT: You CAN get camber/toe adjusters (eccentric bushes) that will 'help' out with the tyre wear, 'apparently'... When I had my VT with SSSL in it, the camber kit did two fiths of **** all... Lucky to have tyres on the back for 20,000kays