Hi Macsup,
My first new board was the 11'6 fly and I was a bit heavier than you are (114kg). I found that within a couple months I outgrew the board and downsized to a 9'10 allwave for surfing. I also purchased the 14' x 29'' glide for flatwater. I tried twice to do some flatwater paddles with the 11'6 fly, but struggled to keep up with the other flatwater oriented boards. In that last year, I have downsized again from the 9'10 allwave to a 9'5 allwave. I am also down to about 106 kg. In saying all that, I still have the 14' x 29" glide and do not plan on getting rid of it anytime soon. The glide has been perfect for me on flatwater, and I love the stability when things get choppy. I never looked at the 12' glide or have paddle one so I can't comment on that board other than that the 14' glide has a recommended weight less than what I weigh now and floats me perfectly well. I suppose what I am getting at is that you will quickly build the balance and stability muscles to be paddling something smaller and could possibly be wishing you had started off on something smaller in the first place. But I am also one for the opinion that we are out there to have fun, not to struggle with standing up. It can be a tough decision!
Another point to consider is that while both the boards you mentioned hold their value, the 11'6 fly might be difficult to sell when you want to downsize. It was for me at least. Due to the size of it, there are not many people that want a board that big. It is, however, a great board to keep and have for friends and family to play around on or introducing people to the sport with.
The glide and the fly are very different shapes. The glide will be great for flatwater and very small surf while the fly will be great for smallish to medium surf with a little bit of flatwater thrown in. In my opinion of course.

One board that I found did both a bit of flatwater and surfing quite well was the 11' Nalu. I've had a chance to demo it twice and if I had the money, I'd be getting one today. It might be a bit tippy starting out, but it is a lot of fun. Another similar board to that is the Hobie 11' x 31.5", which I've had the opportunity to demo and enjoyed it as well.
Anyway, there is some food for thought. Let us know what you end up with, always interested to see what people end up going for once they have all the information.