I'd not recommend running a more powerful pump through an external, if you want more flow put it on another loop, unless you have big issues with head of water between the pump and the tank. If you overpower a filter then you risk issues with the pump driving harder than the flow through the filter chambers can handle, might just cause bypassing in the filter, might throttle things back and damage the filter or the pump.
If it's cheap you're after than I have some from all pond solutions that do an acceptable job. They're a little noisy though, they're also not that easy on the old electricity, but then neither are the eheims.
I'd normally have recommended a powerhead/wavemaker if you just want flow, but I'm guessing there's a reason you asked for external.