Looking at the head vs. flow chart, the 1250 would def outperform the 1048, simply because the curve is a gentle one compared to the 1048 which has a steep drop off. But then again, how do we measure performance gained from using a stronger pump as opposed to a weaker one??
Performance should be proportional to overclocking ability. (quote from a friend
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Performance is also dependent on the components that you choose. No point getting a super pump for the restrictive Cascade block. The Cascade does not require high flow rate for it to reach near peak performance as opposed to the WW. In fact, a negative effect would occur as the stronger pump would dump too much heat into the water.
Choose the pump that is right for your system based on you components. e.g. If u have losta tubing and free flowing blocks, try to get a stronger pump. But make sure your Radiator is up to it in removing the extra heat dumped from the pump. If you utilize a smaller radiator, I suggest that u stick to the smaller 1048.