Biggus, the 2500 mile hypothesis ignores how the V-force actually planned to execute the mission. There was no requirement to recover to their departure airfield; indeed it was prudent to assume that one's home base would have been destroyed.
Then the OP' s paper makes the unwarranted assumption that St Petersburg was an easy target as SAM would not be able to defend a coastal target. Now Kronstaft, last time I looked, no longer had a defensive complex but that could soon be rectified.
The Gulf of Finland is narrow and SAM on either shore can cover the whole Gulf. Finish neutrality is irrelevant.