Sorry, joined this thread late.
My initial query, is are we talking about two tempos (50 bpm and 140 bpm stated in the OP) playing together, or two different meters (17/8 and 5/4) together?
Two tempos is harder.
I have often used two, or three time signatures together in Sonar. Having started out as a jazz and prog musician, I'm currently working on a project where I have to be be more "straight forward". Tonight I have laid down a bass and drum part in 5/4 under the rest of the song in 4/4, as I got bored.
I choose the "Standard" meter, 4/4 in this case, then lay down the other tracks. I sometimes split the "Odd" meter clips to reflect their pulse, where I can. I laid down the drum part, then split the clips every four or so bars, then similar to the bass. This just makes it easier for me when editing/reviewing the song later.
I've happily recorded 4/4, 7/8 and 17/8 together. I've just had to choose my "base" time first, and worked around it.
Now, different/unrelated tempos at the same time, that's a whole new ball game..