I,ve owned both ,the 25 and the 27 ,they are completely different cats ,as the 25 has the upper deck flares molded ,and the 27 has 2 tunnels/deflectors bolted on the deck that were ment to deflect air/water in front of the engines.
the 27 has no sprayrails/lifting strakes on the running surface(last 10 ft) and no notch built into the sponsons,as the 25 has a 15 inch notch,and lifting strakes in its running surface.
I had 4 x 2,4EFI mercury outboards on that 27 ,and 2 x 2,5 EFI (260)on the 25 .
both were built in Kevlar/glass and extremely strong and stiff.
The 25 ran 112 mph ,and the 27 we kept running out of propellor no matter what we put on ...but we were still doing 8000 rpm with 15x34 and 1,87:1 ratio,we didn,t have any bigger pitched props ,and we could not find lower units with 1,75:1 ,later we took one engine off ,and tried with 3 x 2,4 EFI,and still did 7800 rpm with the 15x34,s
I found the 27 Cougar the ucliest cat ever ,and the 25 was looking a lot better IMO