The book shows that all the 790 SMs are 16 front/ 42 rear. The 865 SMs are 16/43. The Americas (all 790) are different at 17/42. Interestingly, the 790 Bonnies are 17/43 (higher rear sprocket than the America) and the 865 Bonnies are 18/43. No doubt it would be best to try going up 1 on the front sprocket. At crusing speed it would drop around 500 rpms I've been told. I just bought a 18T to try on my TA. Fairly easy change keeping stock chain.
