A combination of the Sovvy and the Interpid with the mass of the Galaxy to accommodate long missions...
lets think here for a minute... when before has the Federation used the design template of their best ships to perfect a long-service design...
-looks at the Galaxy- that's right! The Galaxy class was the culmination of SEVERAL different ship designs (case in point the systems they tested on the Pegasus) merged and perfected after many decades of testing - the Ambassador itself BASICALLY being a giant test-bed for the future of the Federation
Why would the Fed's drop a winning system? Hell the Negh'var is basically a bloated K'tinga with traits of the BOP stapled onto it; and then there's the Keldon which is basically the Galor with added attachments to off-set the limited Galor power supply and weapons load - the whole Star Trek Galaxy does this; using designs and features from various different ships (the whole Constitution refit and K'Tinga refit series being examples) to perfect their later designs
For my money the F seems to be a perfect continuation of the Sov that will one day lead to the Enterprise J where the whole secondary hull has been merged with the saucer to streamline the ship. The 'dual necks' and smaller (though stouter) main hull leading to what will eventually lead to the abandonment of the main hull completely
The Enterprise NCC-1701 from the show was the same Enterprise we saw in TMP, WoK, & saw destroyed in TSFS.
The Enterprise NCC-1701-A was an entirely different Constitution class ship, merely given the same name and registry number (with the A added to differentiate in records).
Yes, the Enterprise from TOS and the Enterprise from TMP are one and they same, TMP is the refit of the consistution class then the gets blown up in search for spock then they get the Enterprise A which is also a consisution refit class.
Nope - the original 1701 refit was destroyed in Star Trek III: The Search For Spock - the 1701-A was brand spanking new.
no actually it was the Yorktown renamed Enterprise that's mention in a tech manual somewhere I believe (Mr. Scott's Guide to the Enterprise) Memory Beta mentions the ship being the Ti-Ho and In FASA materials such as the Star Trek IV Sourcebook Update, the ship redesignated as the Enterprise-A was a newly-built vessel that was to be named USS Atlantis , but Memory Alpha says differently I usually go with what the Tech manuals say because they were out before the website was. She was still a new ship but just had a different name before being renamed Enterprise.