What’re your streets / paths like? If you’re spoilt and they’re relatively smooth, smaller wheels could save you a bit of weight and keep your nimbleness.
@moon makes pulleys for 78mm Venom Magnums 
and they’re pretty nice.
Edit - Google check
Tb110 = 2300 grams
78mm Mags = 750 grams…
FWIW, I am switching my gear drive street build with 100mm wheels to belts because ground clearance just isn’t enough, the drives are getting beat to shit, motors too. Also gear drives are heavy, even the ones with POM/nylon gears.
I wish I could comment on motor size, but I’ve never used 50mm motors. 6355 would be fun for startup torque despite the small battery. If you do go gear drive, then maybe smaller motors for better clearance is a good option 
From what I’ve heard, anything smaller than HTD5 is a bad time. Too much skipping and worn out belts.
Where are you from btw? I could sell you my 3ds urethane drives for cheap if you want lol
I would also avoid 50mm motors. Dual 6355 or single 6384 are great for a lightweight board.
I strongly disagree, ya boy rolled around with a single 5065 for months
I’ve rolled around with a single 5065 as well. 
It will work. But your brakes will suuuuck, and I don’t recommend it. If you’re on the lighter end of the bell curve, it may work a lot better for you. I’m around 100kg.
Haha I’m 52 kg 
You took “lightweight street build” to whole 'nother level.
My lightest board was 12 lbs and I had a 5 lbs backpack, only 9 Wh/mi 
I used to commute on a Boosted with 80mm wheels, so that could work. My concern is more clearance issues than bad roads, but if I can get a low enough enclosure, I think the small wheels are still on the table. Smaller is certainly my preference.
That was my experience back when I ran an E-toxx drive on my Trampa. You have to choose between mediocre reduction or having the case get beat to pieces lol, and weight is an issue regardless. I really loved the lack of maintenance though…
6355 with aggressive reduction actually feels quite peppy to me (I’m 66 kg), and that’s on a mountainboard with bindings lol. I’ll look around for a smaller 63mm motor, but I’m fine sticking with a 55 if that’s most convenient.
I’m in the US. Is this a gear system?