Before considering the 40-150mm f/2.8, 100-400mm f/5-6.3, etc. you might want to add some extra weight to your gear bag equal to the lens you want to buy and see if you can easily carry that much weight around.
- 12-200mm f/3.5-6.3: 455g or 1 lb
- 14-150mm f/4-5.6 mark II:284g or 0.6 lbs
- 40-150mm f/2.8: 880g or 1.9 lbs
- 40-150mm f/2.8 + MC-14: 985g or 2.2 lbs
- 75-300mm f/4.8-6.7: 423g or 0.9 lbs
- 100-400mm f/5-6.3 mark II: 1,1300g or 2.9 lbs
I've been having problems with carrying the heavier gear. Last year, I got the 40-150mm f/2.8, 100-400mm f/5-6.3, 7-14mm f/2.8, MC-14, and MC-20. This year after my issues came up, I find more often these lenses stay home. I have specific use cases where each of the lenses will be used, but they don't automatically go into the camera bag. Which is a shame, the 40-150mm produces really pleasing images.
When I started having my issues with the heavier lenses, I bought the 75-300mm as an alternative to the 100-400mm, and I find it is a lot easier to use, particularly on the OM-3. However, it is not splash resistant
Now a lot of people don't like them, but I have gravitated towards using 'super-zoom' lenses. I shot with each of the 14-150mm f/4-5.6 for 7 years each, until I got the 12-200mm f/3.5-6.3. Usually the 12-40mm f/2.8 and the 12-200mm f/3.5-6.3 are the top 2 lenses each year. I like super-zoom lenses for outdoor shots because I don't have to change lenses. This is very useful for things like whale watches, where the whale may be close to the boat or far away, and it will be gone before you can change lenses. While the 12-200mm became my super-zoom of choice, when I got the OM-3, at times I will go back to the 14-150mm f/4-5.6 mark II because it balances better on the OM-3.
I suspect you will likely need to plan to upgrade your gear bag if you get the lens. I find my 40-150m and 100-400mm are too wide and too tall to for many bags meant for smaller gear.
In terms of lenses and grip, I find the 12-40mm f/2.8 is just at the limit of lenses I want to shoot on the OM-3 without an external grip. The 7-14mm f/2.8, 12-200mm f/3.5-6.3, and 75-300mm f/4.8-6.7 are lenses where I can prefer to shoot with a grip, but I can still shoot without it. The 40-150mm f/2.8 and 100-400mm f/5-6.3 I require a grip for shooting.
in looking at my stats, I have not used the 40-150mm f/2.8 with the OM-3.