The keys are not as nice, but certainly not squishy. The button feel of the 48G is near perfect. The 50G tried too hard to look and feel like a TI calc. The 50G is really sluggish when responding to commands, even after the key timing fix. It will drive you mad at first, until you get used to it. I wish HP would fix this.
I have a 48G and a 50G. I bought the 50G after the 48G took a swan dive out of a third story window. It survived (I doubt the 50G would). But I didn't want to chance losing it. The 48G stays at home and the 50G stays at work now.
Your 48SX is still better. The 50G is certainly a capable calculator, but it's got a lot to live up to. The only calculator ever made that could claim to be better than the HP 48S/SX/G/GX was the HP 15C, and even that is comparing RPN apples to RPN oranges.