Way before mid and large arbour reels became the norm I always had larger diameter than required lightweight reels on all my rods. I had a Ryobi 357 magnesium reel (I'd love another) that had 150m of backing and a DT5 on it. It weighed no more than what I currently use, balanced the rod perfectly but had a great retrieve speed.
I also once has a System 3 reel that said that it should take a DT6 and 75m of backing but could barely hold the DT6.
I might be the odd man out here, but I do like a lot of backing on my reels, proper sea dacron at that.
The size of fish has nothing to do with my choice of reel, I used to use a Clan 11' #5 for trout and summer salmon. Weight distribution and line retrieve are much more important to me. My Teton 6 has an SLX #4 and 125m of 20lb sea dacron - it only looks small!