Hey, this depends on what you want, the 250 just give you more option, and definely if a NSR250 or RGV or RS250 runing at the same speed and going through the same corner, same path as the NSR150 then all the 250 will feel safer and more control, confident and power unless you are fitering through the traffic jam then the 150 will be bit more adventage.
The bad thing about the 150 in Australia is exactly what you said, you can push to the limit easily on local street and often that speed and acceleration is not enough to catch up with others not just straight but corner too, it's stock wheel just too thin to have confident in local street specially bumpy road or mountain. In Australia we've got so much mountains, big roads and freeway, is not like bankok where you just fiter , sneek and get these little 20km/hr corner all the time.
And to me is a fun thing of a bike that you can never really know and push to the max limit of it in most situation (except for straight i guess), so there is always something to discover, learn and soemthing you cannot perfect so you never get bored of the bike, thats what the NSR give me, loads of fun.
After all is what you want, if you after strong performance like a NSR250 then you might be diappointed with the 150, if for a realiable and strong traffic fitering bike, i think 150 should be the choice . However, if you are really after something that you can push to it's limit all the time, then you should get a 50cc scooter........
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MC28, Repsol