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.