Pressure Washer Pump Question

[RickDel 14]

Hello, I'm in the process of buying a pro-sumer model pressure washer. I've narrowed it down to two different models with two different pumps.

1. A General TX1510A (built-in unloader - 4 GPM)

2. A Cat 66DX (external unloader - 3.5 GPM)

The model with the Cat is $300 more expensive, so I have a pump questions to help with my decision.

How will I notice the “better pump”? Will the General Pump slowly lose pressure or will it just die?? It seems to me that If it doesn't gradually lose pressure, then there's really no difference between pumps until they die, and in that case, I could buy a replacement General Pump for the difference in the initial price.

Thanks!