Ok so, the MT10 is a great bike no mistaking that at all. Great upright seating position, even better with the optional comfort seat. Handling is very good, turns in pretty quick in corners and then easily flicks over the other way. Engine sounds great especially with a decat, although it can 'drone' a little when just cruising. Power delivery is fab too, although get ready for the front end lifting all the time in the first 3 gears, with it's short wheel base i've come out of corners still leaning with the front lifting up. Throttle is snatchy from the factory, but a remap can sort that out. Fuel range isn't that great, i've had the fuel light flashing at 90 miles when out for a 'spirited' ride. Pillion is not comfy, this comes from a riding friend and my wife. Longer footrests help from the tracer 900.
SDGT 1290, seating position is very similar to the MT10, although maybe 1.5-2" taller seat height. Fuel range is good. I recently did 175 miles and range said i had about 50 miles left, although not sure how far i could push it. Some owners say 220-240 per tank is acheivable. Front screen is adjustable, but doesn't seem to make any difference, in it's lowest psoition wind hits my chest and not my helmet which is good. Handling feels pretty good, still getting used to this bike but i'm confident it'll keep with the MT.
Overall, the MT10 is perfectly capable of doing everything, just the short tank range lets it down for. It is a greedy engine. Personally i think the SDGT just edges it though, it just feels more like a do everything bike with good range, comfy, good styling (imo). I'd say if you can test ride both.
If there's anything specific you want to know just ask
