Masterpiece is strong in slogs, as is Silk Road. Would trying to consistently nab Silk Roads be more or less profitable than using P-Stone to spike the occasional Province?
I don't think so. Getting good value out of Silk Roads takes a lot of work. The 1 VP per 4 VP cards is actually pretty harsh compared to Vineyards' 1 VP per 3 action cards.
If you get like 6 Silk Roads, 4 Duchies and 4 Estates, that's still only 34 points, worse than 6 Provinces.
Normally you would have a decent chance against a normal BM deck which has a lot of trouble clearing out the last Provinces, but a Philosopher's stone deck gets increasingly better at buying Provinces. Especially with Scavenger and frequent shuffles, it's basically a Province every time you have a PS in your hand.
On this particular board I would probably open Scavenger (a good card in its own right)/Scheme and get a Potion on my first shuffle.
With Scavengers, I would put Potion on top. I think a deck like this can handle one or two more Scavengers. Possible terminal collision is not so worse compared to the upside of having multiple Scavengers.