On most sights the bigger fiber will be brighter. Alot of folks don't like .029 for longer yardages....but if its low light your worried about, you won't be shooting a long ways anyhow (most likely). Probably if you have an.029 on your top pin (20 yd?) and you should be fine. On my sight I can see my top pinpast the time where I can see the deeranyhow, soI would think you should be fine.