Russia

[Slaists]

after the 3rd gift or so i realised that it wasnt increasing the boost really - but is it really the case that all the levels of gift give the same (maximum) boost of 100? is there any benefit to using a more expensive gift then?

Not really, it's bugged for now (or a stupid feature). All gifts give +100 (you can test it: just save your game before the test and see what each level gives to your relationship when you give it to a nation that has not received any gift from you earlier). So, unless you have a good reason for wanting to waste some ducats: just stick with 2500.

Unrelated: some posts here suggests that the Russian starting Cossack infantry cannot use later infantry drills. They actually can. They can use square fomations and can learn fire by rank. They do not get bayonets though.