My HTC One M7 has a 4.7" screen. I think 4.5" would be the bomb. I have been looking at the Sony Z5 Compact as a replacement. But I just replaced the USB port again on mine, so it should last until next years new models come out.

I have no use for a larger screen. 4.7" is ok, but I still have to stretch my thumb to reach one handed. 4.5" I think would shrink it just enough to make it work out fine. The Sony is thinner too, and with a thinner case, it would also make a big difference. I had to put a blocky case on this one because without it, it has sharp edges and is too slippery. It would have taken too many falls by now to be recognizable.