Considering you live in London and can use the bike to commute the smaller capacity bike will be an absolute pleasure. I commute up with my XJ900 every so often and london traffic on a big bike sux. I did once use a TW125 to get through London and it was fantastic in comparison. If you are really stuck behind a car you can just lift up the front end into a gap, jump kerbs etc. Small capacity is more than adequate for city riding especially considering you will never get above 30mph anyway.
I'm not saying get a 125...but get a dirt cheap 350, ride it for 3-6 month to get the confidence/experience and then go ride as many of the bikes on your wish list as you can before making the final decision. You will be surprised at how your dream bike might just feel wrong and a bike you never considered will feel perfect.
Then again if you have no intention of commuting and want to get into serious distances straight off then I would consider getting a bigger capacity mile eater.
happy hunting
|