Jackeen, I have a 5.05 Gemini with hypalon tubes and it's a great boat.
Its got an 85 CV Yamaha 2 stroke on the back and it goes pretty well although may be a little underpowered.
The only issue I have is that when on the plane, in high cross winds, wind does tend to get under the tubes and lift them a alittle, particularly when banking the boat on a corner...
Nothing to worry about but a liuttle unsettling the first few times.
But it has been out in 4m pacific swells this year and handled them pretty well even with a relatively inexperienced (me) person at the helm.
The newer ones (2001 onwards) have larger tubes than my 2000 model and apparently the stability has improved.
Some say that the 5.5 is a better boat for big chop and that was originally what I was looking for but i got a great deal on mine so went for it...
It hasn't disappointed me , let me down so far.
i guess you've seen this page from the Gemini site?
let me know if you want more details...