I own a Farr 11.6 and have raced on and against Beneteau 375's. The Farr 11.6 will out perform the Beneteau boat for boat on all points of sail, and pretty much all conditions light to heavy. The Farr 11.6 is easier to handle, can be raced by a smaller crew (less weight needed on the rail or for sail handling) and is easier to keep at speed in changeable conditions than the 375. Like a lot of IOR derived designs of that era, the 375 loses speed easily and its hard to get it back again.
Compared to modern designs the Farr does not point as high and is a bit stickier in really light stuff, but compared to the 375 there is no contest boat for boat. But of course, if you plan to race, the real question is how the two boats are treated under your rating rules.
As for cruising ability, the Farr 11.6 has less headroom than the Beneteau 375 and is visibly less plush. The interior layout and tankage on the Farr 11.6's vary widely depending on when and where they were built. They typiccally have a very similar layout to the Beneteau 375 head forward version except they do not have the 'aft compartment' option that some of the 375's came with. The Farr 11.6's typically carry 80 gallons of water, which is more than the stock 375, but carry less fuel. Frankly the stock Farr 11.6 fuel tankage is absurdly small and so they often get fitted out with an extra 20-25 gal blatter forward of the starboard water tank.
The Farr's typically were set with three seaberths each side aft of the main bulkhead, which is really nice for distance racing but less convenient for family cruising.
Build quaility wise, the Farr's are surprisingly robust for their light weight. They typically have almost no liners making them easy to work on and inspect. They are not cored and so depend on a complex system of glassed in frames and structural interior components. Even when pushed hard there is no sense of flexing. I have worked on Beneteaus of this era and they are harder to maintain with their near full liners and are known for their wracking.
The one word of caution on the Farr 11.6's is that there were a number of Farr 11.6's that were built in Australia with 'optimized keels' that were very different than the original Farr design. In the original form, there was a reasonably deep sump, with pretty massive width and and depth transverse frames. (which is part of the reason that they do not have all that much headroom). In discussions with the Farr office, they indicated that these boats with the modified keel design and structure were not engineered by the Farr office and were unauthorized pirated versions that were built with IMS style fins or with bulb keels, and without the deep sump and the frames that were part of the original design. These boats also had a completely different laminate schedule and a simplified framing system as compared to the original design. One of these boats,
Rising Farrster, lost its keel, killing the crew. The link to the coroner's report and update can be found here:
Updated - Implications for Yacht Owners Arising from the NSW Coronial Inquest into the Deaths Aboard the Yacht Rising Farrster
These are very different boats structurally than the Farr engineered 11.6's and although they offer better upwind sailing capabilities, they should be avoided.
Good luck,
Jeff