After the increase, he can lift 300+50=<<300+50=350>>350 pounds
Decreasing the distance increase the amount he can lift by 350*.3=<<350*.3=105>>105 pounds
So he can lift 350+105=<<350+105=455>>455 for 10 feet
The straps add another 455*.2=<<455*.2=91>>91 pounds
So his total weight is 455+91=<<455+91=546>>546 pounds per hand
#### 546