I think you should just set the Bossa style to whatever tempo you feel comfortable at playing. If you have a recording of say, Girl from Ipanema, play it and start your KN style and adjust the tempo by trial and error until the two are about the same. I don't know if the KN1400 has the 'Tap Tempo' facility but if it has, this is a good way to set the keyboard's tempo to that of a recording you are listening to. Because of the way the older KNs had the Bossa style configured, The Tap Tempo function may result in 'half tempo' or 'double tempo'. However, it will be obvious when you start the style playing and you can make the appropriate correction. Some Bossa Novas seem to be better played a little faster than others eg 'One Note Samba'
I don't quite understand what you mean by "Then for every bar of Bossanova rhythm, I would play two bars of melody plus accomp in it. I felt there is more bossa feel this way." I feel the song would not sound right if it was played that way. It should certainly be played bar for bar. If you say that t=70 is too slow, just try increasing until it sound OK to you. If you don't have any bossa nova recordings to listen to, drop me an email and I'll send you an MP3 of one which is recorded on KN7000. The Technics files recorded on KN7000 will not play on KN1400.
------------------
Willum
_________________________
Willum
After silence, that which comes nearest to expressing the inexpressible is Music.
Aldous Huxley
( especially when the music is played on a KN7000....)