Jon is correct that the longer fin will noticeably improve the stability of the board. Both the F-18 and the XBC Fish come with removable fins. The XBC comes standard with Future's fins. This brand is my favorite, plus you can get fins from as small as 3.25" up to 5 something - larger than you'd ever need behind the boat. The XBC Fish also is configured as a thruster with three fins, whereas the F-18 is a twin fin.
The F-18 is more comparable to the XBC Grom in 4'9". I would suggest that probably the Composite X in 5'0" is a better choice than the F-18 in your situtaion. The issue with the F-18 is that EVERYTHING is custom. The rocker, length, width, fin boxes, etc. It's pretty tough to make those determinations at a beginner to intermediate level. The Composite X in the 5'0" length will come in stock size and shape.
Two additional boards I would recommend you consider are the Shred Stix Piranaha and the newly reconfigured Inland Surfer Blue in a 5'4"
The XBC fish and Comp X will be considerable faster than the Ride. With the the removable fins you'll be able to customize the feel with different depth fins, starting with longer ones and working down to shorter ones.
If you've truly limited yur choice between the F-18 and XBC Fish, you'll be happier with the XBC. If you're still in the descision making phase, the XBC Fish, Walker Composite X, Inland's new 5'4" Blue or Shred Stixx Piranaha are all decent boards worth your consideration.
I think I may have done a product review on the XBC Fish, I'll check in a moment.