Peter I had springs with 120Lbs seated and 390Lbs/Inch and it was NOT enough to prevent valve float probably due to the heavy (lots of inertia) hydraulic roller lifters. Valve float occurred at 5200 rpm. I updated with 155Lbs seated and 427Lbs/Inch and revs to 6500+ rpm without floating now. I use a Lunati wodoo hydraulic roller cam fyi and full synthetic oil 5w-30 and standard flow/press blue printed oil pump.
The reason I chose the 120/390 springs from the beginning was my concern about the lifters collapsing but that proved to be insignificant in this case. And the tech support from Lunati Cams advised me that they recommended the 120Lbs but obviously that was a load of BS and caused me lots of headache in the troubleshooting.
So don't be afraid of going with 150lbs seated and of course use stiff push rods and valve geometri to suit.
On a note, had I known what I know now I would not have chosen hydraulic lifters but gone for solid rollers in stead and just done an annual valve play adjust ;-)