I don't know your exact gear cluster set, so I'll just post results for your 1st and 6th gear. All speeds are ±1MPH.
[44, 30, 10T]
1st gear: 9MPH @ 4500 (torque peak), 14MPH @ 7000 (horsepower peak)
6th gear: 18MPH @ 4500, 28MPH @ 7000RPM
The SBP gears you posted are for the 2-stroke kit tho. The 4-stroke kit comes with a 48T outer, 30T inner, and a 10T j/s output standard. Ofc, the gears can be substituted. I recommend using a 48T outer crank, 36T inner crank, and 10T jackshaft output. I use those gears on my 4-stroke shifter, and the ratios are fine. Here's what you'd be running with those gears:
[48, 36, 10T]
1st gear: 11MPH @ 4500RPM, 17MPH @ 7000RPM
6th gear: 22MPH @ 4500, 34MPH @ 7000
As you see, with the 2nd set of gears, you get a better cruising speed and still have a lot of hillclimbing ability.
Hope this helps.