If you fz150 user any 250 cc is pretty plentiful actually.

It's fast and more importantly manageable handling.

Faster bike means bigger bike. Bigger bike means harder to handle. It also mean more dangerous for you and makes you slower.

My suggestion is go for 250 cc less
As this type is city friendly and you still can outrun those modi kapchai

250cc is pretty much can do all that.

R25 seem ok but i never used one. So no comment.
Z250 is pretty fast. Not sure about duke 200 or ns 200.

But last week on my way to work. This duke pass me super fast and he keep speeding. But the z250 pretty much keep up with it easily. If you can get used duke. I think its a bargain tho. It's pretty cheap.