Couldn't find the specs on a Rio 1800 but on
www.aquatictech.com I found out the Rio 1700 does 352
gph with a 4ft head and the Rio 2100 does 529
gph with a 4ft head so it's probably somewhere in that range.
Without knowing for sure what your overflow can handle I wouldn't get a much more powerful pump
IMO.
Is your overflow drilled or
hob? One or two holes and what size are they? (inside diameter)
Since the Proclear 125 Wet/Dry is rated for 450
GPH flow rates I'd stick with a pump that doesn't exceed that with a 4ft head. Unless you plan on upgrading your sump as well.
If your current pump isn't breaking down on you or is excessively noisy then it's probably the best fit for your current setup.