Dimitri , A 5 mtr RIB with a 115 bhp engine will go like a rocket (what pich prop you have on??).
For your benefit now please note that I use to have a GEMINI 5.05 and I had a 75 bhp very old Mariner (1991) on board with very many hours trawling and cruising. The boat and engine went like a dream. With a 19" AL original prop it was doing 45 knots @ 5,500 revs full trim with 2 people onboard and 140 ltrs of fuel, full load and light chop in the Aegean and with a 17" AL prop it was giving 38 knots @ 5500 revs full trim same conditions as before, however as you would expect acceleration and pull was much much better than with the 19" prop.
The engine excpet having problems with the trim motor (had to repair it every summer because the new one comes with the bracket and costs as much as an engine more or less) nothing else happened and I sailed the boat a lot.
Consumption for the 75bhp Mariner about 1 ltr/mile (normal staff) doing 3500-4000 revs with both props.
In have now a 7mtr boat with a 200bhp Yam VMax different ball game altogether (F A S T VERY VERY VERY F A S T 65knots @ 5800 revs full trim and light load and 21" pich prop!!- will change it now for a VIPER 23" and will try also a 25" see what happens).
Now for the benefit of the thread I believe that all two stroke engines these days have more or less same endurance and reliability unless of course you are lucky enough to get the 'Friday the 13' engine. Then it doesn't matter what make you've got.
A Merc or Mariner are good, very good infact.
I have heard bad comments about the electrics and fuel supply for the Envinrude Fihts but never owed one.
Finally, knowing that all Mercs and Mariners suffer from trim problems, I would make just sure that the trim motor hasn't been opened and is in tip top condition. If this wasn't the case I wouldn't touch one. As I said it costs faaar tooooo much to change it and repairing it is not an option unless one is desparate (like I was).
Hope this little wafle could assit .
......and Scotty since you are in Greece why don't you pass by and check out the Falcon is MUCH MUCH better and more competitively priced that the Zodiac.