Hi guys,
It's me again, with a new "strange tactics". (Luca's words in a private message)
But first a few words:
1) This explanation task is not as easy as intermediate was, anyway i'm doing my best.
2) The key point of this strategy is: "Avoid swinging". Swing is the public enemy nº1 of any sweeper and with such a grid configuration it is so easy do it!!!!! The best weapons to avoid swinging are:
            a- Flag horizontally and sweep vertically, in order to perform the shortest possible path.
            b- Flag and sweep sectors. Once they are finished you don't need to go there anymore!!!!!
3) Be patient, fast scores like 61s, 62s ... will appear around day 5 or 6.
4) Feel free to make any comments and suggestions about this post.

Hexx Expert strategy

- Flagged.
I think this is obvious, the low mine density (50%) makes virtually impossible a fast non-flagged or flagged/non-flagged strategy.
Flag all mines except the last ones.(I left out only the last 3 or 4 mines when i managed 55.37)

Sweep and flag right sector.
It is the most important step. The advantage of starting at this sector is that it is easier to see clues given by numbers, in other words, it has the most potential. Present day, i recommend less than 20s to perform this step.(see missed 14s screenshot, my best right sector performance)
Place the mouse cursor at right bottom corner and start moving using a combination of horizontal flagging(rows) and vertical sweeping(columns) according to this sequence:
A) Sweep right edge and the adjacent unmined box of the first mined block at top edge.
B) Move back, flag edged mines revealed in A, including the first mined block at bottom edge and then sweep it's adjacent unmined box.
C) From bottom to top, flag horizontally the first mined block of each row that have an right edged mine and/or sweep it's adjacent unmined box. Note- In the below screenshot, the mined blocks that have an right edged are marked with a grey square.
D) Flag and/or sweep right columns from right to left.



DEMO VIDEOS
See these demo videos of STEP 1
(note: press right button and then choose save target as....)
http://www.free-webspace.biz/nonosw/expert.zip

TIPS:
1- VERY IMPORTANT, look at the board's left edge at the time you finish A, if you find out a perfect pattern like 7-2-1, 5-3-2, 3-2-2-2 etc... (best scenario) or an easy one with a large mined block like 10, 8-2, 7-2, 5-5 etc..., you should move to left sector at the end of STEP1 and repeat STEP1(mirrored).
2- C and D are vital to the success of this strategy, so make sure you flag horizontally from bottom to top and sweep vertically from right to left. (Otherwise you are swinging!)
3- C and D can be done at the same time.
4- Think at C and D.
5- Keep doing C and D as long as you can, even at STEP 2. (note: It is possible to finish the game this way!!!!!!, but it doesn't happen so often).
6- In A use guessing when you have patterns like 7-3, 5-5, 6-2-1, 3-3-3, 4-2-1-1 and so on...
7- If you get stuck in the middle of STEP 1 and there is a perfect pattern at the left edge, don't think twice, just move to left sector immediately!
8- Pattern recognition is always useful.
9- Make sure that the field left behind has no unmined boxes to be revealed.


Sweep and flag center and left sectors.
This area should be a square or something close to it. Due to its "symmetry" it is possible to avoid swinging.(see missed 24s screenshot)
At this stage, there is no special tactics.

TIPS
1- At left sector, use TIP 1 of STEP 1.(very important)
2- At center sector, keep using C and D as new mined blocks are being revealed. It is not rare to "clean-up" all center sector this way.
3- Get mine position info by using top and bottom edges and pattern recognition.
4- Pay attention to simple patterns like 2-1, 3-2, 2-1-1, 3,  etc.. because sometimes they are already flagged, all you have to do is to sweep.
5- Avoid guessing or at least use it as last option.




Ideal path at step 1