T450 has 130dpi, T550 has 140dpi. It is small but noticeable difference.
It is a software problem that for pragmatic reasons I don't want to get into. Good luck setting non-integer scaling on current operating systems (like 1.25 or 1.50). It's either not supported, or the effect is blurry. It's a different story for retina screens, you set scaling to 2.00 and you're fine. But I was talking about non-retina.
I am surprsied reading those comments. A touchpad on my x250 is fantastic and very customizable. I hate touchpads in general but after customizing it to be very sensitive and proper dead zones (to avoid clicking on accident in areas I often put a part of my hands) even started to like it.
I customized to very low sensitivity and I use only for clicking these days as trackpoint is just much better an interface.
IMO Touchpads/clickpads on those are a deal breaker. They are so bad that it is almost impossible to be nearly as productive as with a mouse.
On the other hand, Apple really got the clickpad right.