I decided to just bite the bullet and figure it out myself... Modifying my second solution for a bigger game:
Trash Colony with a TFB card like Remodel to gain a Border Village, which you use to gain the last Silk Road. The Border Village puts you up to a multiple of 3 action cards, powering up your Vineyards. Colony into Border Village + Silk Road means your deck has 1 more card overall, and it just so happens that this bumps you up to a new multiple of 10, powering up your Gardens. Also, that Border Village was the first one you got, bumping you up to a new multiple of 5 differently named cards.
Suppose you previously had 12 Fairgrounds, 12 Vineyards, 12 Gardens and 11 Silk Roads. Note that this is possible because you need to 4-pile in a game with 6 players.
-10 VP from losing a Colony
+24 VP from powering up Fairgrounds
+12 VP from powering up Vineyards
+12 VP from powering up Gardens
= +38 VP net gain.
But you also get more VP from gaining the Silk Road.
Silk Road's worth stays the same because you lost a Colony and gained a Silk Road, so the total number of VP cards remains unchanged. The exact worth of the final Silk Road is variable though. The maximum I can determine:
Kingdom includes Vineyard, Fairgrounds, Gardens, Silk Road, Border Village, Great Hall, Harem, Tunnel, Duke, Farmland.
Note that the only Action cards in this set are Border Village and Great Hall. Without depleting the pile you could have 11 Great Hall; grabbing the single Border Village bumps you up to 12 Actions, a multiple of 3, to round out the Vineyards.
Having every card in the Kingdom (minus Border Village) = 9 differently named cards. Also throw in Estate, Duchy, Province and Colony for 14. Copper, Silver, Gold and Platinum bump that up to 19, so adding in the single Border Village would push it to 20 to round out Fairgrounds.
As far as Gardens go, we can add or subtract the treasures to make sure the gains round those out as well.
Since all the constraints from my solution are now satisfied, by the end you could have:
12 each of Fairgrounds, Vineyards, Gardens and Silk Roads
11 each of Great Hall, Harem, Tunnel, Duke, Farmland, Estate, Duchy, Province
10 Colonies (1 was trashed, and 1 remains unpurchased to prevent ending on piles)
= 12*4 + 11*8 + 10 = 146 VP cards
Meaning that the SR gained at the end is worth 36 VP.
The total net gain is thus +74 VP.