slant valve springs

for spring pressure recommendations,, I would go with what the cam supplier recommends.
A custom cam grinder like Oregon will have in house experts,, a major cam supplier like Comp will have a Tech line. They would be familiar with the ramp rates and what it will take to control the valve. Modern cam profiles can have pretty fast ramp rates,, that is how they increase performance, the valve opens opens and closes (ramps) faster,
The risk with too low of a spring pressure is that there can be valve bounce at the seat when closing. That shock is not good for either the seat or the keeper grooves.

If your cam supplier is not concerned over spring pressure,, you have either a conservative cam profile or the cam lobe was made from an older master with slow ramp rates.