For pulling cars, etc up a hill or onto a trailer a 4,500lb unit isn't going to cut it. At best it will be adequate. But you can add a snatch block to reduce the load on the winch.
The 8,000lb harbor freight unit gets surprisingly good reviews, but the remote controls are the weak point (contacts inside don't last very long). I've used the 12k lb unit before and it still performed well even when maxed out.
If you can wait and save up the extra $, get an 8,000lb unit at the least. You'll find new uses for it all the time.
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