Smurf, welcome onboard.
One of the things i noticed as a great difference is the way the engine runs.
As the review in today's
BIKE also mentions, the Street triple is very low geared. That means a lot of gearshifts.
The MT do city and country roads with bravour with out an instant stir in the gearbox, also because it have got the greater momentum.
Sound wise, i clearly prefer the MT, not to mention the exhaust with is much more refined and sporty on MT

Mileage on the MT is at least 15-20% better (depends on your right hand though...) than the Street Triple. You might fear, that the fuel tank is too small on the MT; the fact is, that the 17.4 litre tank runs out at about the same milage as the MT. You've then saved 3 litres for each tank - that is worth taking into account too?
Finally, service costs are tremendious high on a Triumph. Look for 350-£500 for each service. ouch!
I have just got the first done at SMC in Sheffield. Yamaha pays first services labour, you pay the oil and filter + you get data tag added for FREE.
My '12 Street Triple R developed a leak of coolant; dealer had to open engine at 2800 miles, and struggled to put it together, as they couldn't get the right gaskets. That is worrying to hear for their most famous engine.
Battery went dead at first winter, because Triumph is VERY sensitive to the voltage output, and simply refuse to start.
The MT compared starts almost just by looking at the start button!
Seating is a different story. I'm a full grown adult with ...erm.. a bit extra on the side bones

The tank on the Street Triple felt being in the way, you lean over the tank.
MT is much more gently and let you move around easily.
Another thing i have noticed, is how sharp the two bikes can turn.
With the Street Triple, a u-turn on the road becomes a 22-point turn.... to complete the u-turn without reversing, it will have to be on a dual carriage road

The MT is not fully as a supermotard, but it surely can make a good turn - which is also great for cornering at low speed, slides and drifts - not that i'd ever do that
But get out there and get a good test ride, come back with a huge smile and make your decision
