In FASA lore the D-10 was the "Queen of Battle" during the Four Years war also this is the same period that Federation hero and fleet captain Garth of Izar made his name as a bane to the Klingon advances near the planet Axanar. So depending on where you start TOS (before or after Captain Pike of NCC 1701), it could be a candidate for late Pre-TOS.
What I personally don't agree with is that in FASA Trek the D-10 was supposed to be the Klingon threat to the pre/TOS Connies. The Klingons already had the D-6 and later the D-7 to counter the Federation Constitution class ships.
FASA lore aside, the D-10 is an excellent multi-role ship. It can be fitted to be a medium carrier, heavy troop transport or even a standard battlecruiser. Its not a supership and can use off the shelf D-7/K't'inga parts available in the Empire and if given a cloaking device, it adds an extra level of strategic options that FASA Trek never explored despite their heavy use of the Klingon-Romulan technology exchange treaty.
Although the FASA Trek universe makes this a pre/TOS ship, I prefer to make it a TMP era ship that was built either before the Excelsior class or as a direct response to it.
FASA Trek was very wacked when it comes to ships. Another shining example of inconsistent design is that the D-10 H has a non-torpedo armed L-9 Saber command pod and that was supposed to be an upgrade!!! I have a very hard time with non-torpedo armed ship-of-the-line Klingon ships.
Klingon Academy gave the Klingons Heavy Torpedoes as a racial weapon but even KA has some things that don't sit well with me either. Not every ship larger than a heavy cruiser in the Klingon Empire needs to cloak...
Now I have always held that FASA Trek can be just about dropped into the SFB timeline with little or no significant alteration to the SFB timeline. At least the SFB timeline tries not to contradict itself.
That is my opinion and your mileage may vary...