Do you mean far enough for the resolution (blockiness), or for the screen diameter (immersion)?
For computer monitors, 1.0-1.5x monitor diameter is the recommended distance. So for a 40"-43" monitor, you'd be looking at ~100cm-160cm.
For a quick-and-dirty test for your own preference, you can calculate the relative distance with your current setup, and compare it to the new setup. For example, an eye-to-monitor distance of 70cm with your current monitor would be roughly identical to looking at a 40" monitor from a 1m distance (with the same resolution).
Personal experience:
About a year ago I was still using a 42" 1080p HDTV from a 1m distance, so slightly closer than what is recommended. But it was actually good for me. I've since moved on to a 144Hz FreeSync monitor, but the biggest they got was 32". Looking at it from a 75cm distance, even though I would have 30cm more room on the desk. Wishing that someday they'll make a ~40" 1080p 100Hz+ FreeSync monitor. Or 4k, if they ever manage to get all the scaling issues sorted out...