This is such a fantastic lens, I couldn't consider giving it anything less than five stars, but you knew that anyway. The reason you're reading this review is that you've got an E5 and you've already bought a 14-35 lens, and you've been so incredibly impressed with it that it's now your main lens, and you've put your 12-60 to one side because you never use it, and though you're happy with your 50 to 200 lens you're now wondering whether it's worth the cost and the weight to upgrade to this. Let me tell you straight away, that I don't think I can advise you, but if you're interested, let me tell you my story, and see if it helps.
I've always been an Olympus person. I started in the seventies with OM1 and OM2s, and it was natural when I started with digital that I should get an E10 then an E20. This was the point at which digital became better on balance than film, and I made a definite choice at this point to stay with Olympus simply because they had the 4/3rds format, when everyone else was going letterbox. I started with and E3, and upgraded in a half-hearted way to an E5, using the standard 12-60, plus the very long but basic 70-300. Suddenly though the sensors in cameras had become better, and I could so easily see the flaws in the 70-300. I got the 50-200, and was delighted to find that at 200 on the new lens I could capture more detail than at 300 on the old lens. The 50 to 200 was almost as good as the 12-60 throughout it's range.
Then I toyed with the idea of the 14-35. I didn't believe it could improve on the 12-60, because in my eyes the pictures it took were flawless. In the end I gave in, and within a week I realised that they gain wasn't better definition, it was instead brilliant contrast and brilliant colours. Now I'm never without this lens - it's the best lens that I've ever owned, and possible will ever in the future. I use it endlessly.
The next step for me was the 7-14, which is another of Olympus' top pro lenses. It makes me anxious to use it, as there is no possibility of a protective lens, as the glass sticks out so much. However, I've had such fun with it. It's a brilliant ultra wide lens, takes photos that are full of life and colour, and get you right into the action - just plain good fun.
So, in my move to getting top pro lenses, I next bought the 70mm macro lens. Yes, it can be used for portraits, but it's really too long for convenience. And indeed, it does do good macro, though be aware that you do need to get a proper flash - those LED ones don't cut the mustard - all the antishake in the world doesn't cope with a macro lens, and your only solution is to stop the motion with a sharp flash. Yes, its a technically great and light lens, but I've never really got any true pleasure from it...
... and thus I've come to this lens. I've bought one now, and have done all the stuff you do - comparisons with the 50 - 200. At 200, there's more detail than in the 35-100 at 100. That's inevitable really as the 50 - 200 is pixel sharp. And even with a 2x converter, which I have, the 5-100 is no sharper at the top end, though a little bit brighter. But this time I know what I'm looking for. Not end of the lens detail, but the same contrast and brightness and colour in my pictures that I found with the 14-35. This lens delivers it all. I've been using it at dawn and dusk, for badgers and foxes, with great results. Oh, and guillemots too, though they sadly are just a bit too far away! I'm really pleased with it, and wish I hadn't waited so long to get it. It is rather heavy, but not impossibly so. It's not something that you'd choose to go out walking with, but if you've got a shot in mind, it's certainly worth carrying it, and the weight of the lens is near the far end of the camera, which means it's easy to hold steady.
This is a lens that's at the end of a line, and I know that I'll have to move on one day. Some people say that this isn't for someone who isn't a fully fledged professional photographer, but if you enjoy photography and want to extend the quality of your photos beyond the mid-range, then I'd reluctantly say to you that yes, this lens is worth having.