I agree you won't be able to feel the difference of 750 lbs.
If you're in the market for a new car anyway, you may want to consider a lighter vehicle, if that lighter vehicle meets your needs; but I wouldn't go out and by another vehicle if I was happy with my current one just to save 750 lbs.
The first year we had our motorhome, we towed a full-size, extended cab, 4WD pickup weighing about 5600 lbs. We now tow a Saturn Vue that weighs in at about 4000 lbs. The 1600 lb. difference was definitely noticeable (especially uphill as Gary says), but not earth shattering. Gas mileage is about .2 mpg better with the lighter Vue.
If I understand correctly what you're asking about the brake systems is you want to try the ReadyBrake surge brake; but if it doesn't work, you are asking if you can add a "brake in a box." If the ready brake doesn't work, I would just eliminate it from the tow bar setup and use the brake in a box instead. You may want to try a search on this forum for "ReadyBrake" to see if you can find any opinions before you buy.
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