Think im going to agree with some opinions here the difference betwen a 120/140 is only going to be minimal. I think im a beliver in a do it all bike my case a heckler and a hardtail or some such play bike, in my case just to let me know what it was like when i started this hobby back in the 90's. (New BeFe order'd this week for just such a reminder lol.)
Think you should stick with the 140 bike for everything and get a nice hardtail play bike for the rest razzing, D?H etc just to get your skills dialed.
Other than that just ride you can only ride one bike at a time after all!
Bat.