I'm going to point out that, in my experience, a mild turbo setup won't need the added spring pressure.
Once you start pushing over 18 PSI through the system(especially with a restrictive 'stock' turbo), that's when you really need the added spring pressure.
Pretty sure this also requires a bigger-than-90CC IP to do, too.
On my '88, I didn't start having valve train issues until I went with a 110CC pump and cranked it up enough to give me around 22 PSI from a TE06H turbo - Going up a hill at WOT, the massive exhaust back pressure held the valve open enough that the lifter 'pumped up' just a hair, the valve hit the piston, and bent the pushrod.
Ended up doing this a couple of times under the same WOT condition before I finally swapped in stronger springs(Only the exhaust pushrod bent).
Mind that I had been running around with a 90CC pump and then a 110CC pump for a couple of years before this with no issues, pushing 15-ish PSI.
What I'm saying is that while the stronger springs are an upgrade, they are in no way critical for a turbo. Only if you are going for massive power(>250 HP at the wheels, or about double the stock NA HP) do you really need to worry about it.