By lowerig th kv & running on limited voltage, you have really limited the motors power output potentials...the amperage will fry it as you have learned.
In a "best case" senario, these motors are on the edge at 5kw sustained.
do you have a reliable meter to moniter what the amp draws are in use?
given the info above, I would think it should run well with an sustained 2kw input with acceleration peaks of less than 8kw's.
it is important to have a moniter (cycle anilyst is nice) as the XieChang based controllers will overshoot their programed rating by a fair margine under acceleration.
Also, by my math your over geared. 4.3-1=100+ kph.
I would recomend getting it down to 6.75-1 reduction.....that still works out to 70kph unloaded....you will be amazed at the kick in the pants with proper gearing.
I need to really hit the books & memorize the motor math someday....I hate blathering info with no quantifiable data to back it up....all I have is the seat of my pants & 30# of scrap wire from re-winds