if you're not hit capped with dying curse, use the focus stone. i'd say. armory seems to be buggy for me so i can't get to your page properly.

Haste can be a tough thing to balance for a boomkin.  I personally believe Dying curse to be the better trinket of the 2, for 2 reasons:
a) Spellpower is always going to be stronger than haste, stat for stat
b) A randomly procced haste buff is not going to be as generally beneficial as a randomly procced SP buff

Let me elaborate:  
The haste soft cap (this is not a hard cap in the slightest) is in place and generally accepted because after 400 haste the GCD (global cooldown) of wrath is affected while Nature's Grace is up.  A normal boomkin  should see an uptime of Nature's grace at about 50% (probably more).  What happens is: while Nature's Grace is active (assuming the druid has approximately 400 haste) the wrath cast is faster than the 1 second global cooldown of all spells.  This means that each wrath cast, will actually take longer to cast than the Nature's Grace buff suggests.  In effect, lowering your dps as a whole.  Now this is of course, assuming you are using a Lunar based rotation.  
So when using the Elemental Focus Stone, the proc will often occur during the wrath casting phase of your rotation (about 30%).  effectively making the haste buff useless during that time.  However an SP proc will always be useful regardless of the timing in relation to your rotation.  And when dealing with a randomly procced buff, utility is key.

Also going with the understanding that SP is inherently a stronger stat than haste, if i recall correctly, SP =1, Haste=.6 (or .8, I can't remember offhand);
Dying Curse has a procc that triggers 765 SP for 10 secs, and the Elemental Focusing Stone has a Procc that triggers 522 haste for 10 secs.  That right there tells me that I should pick Dying Curse over the Elemenetal Focusing Stone.
From one Boomkin to another, I hope that helps.
Also: 400 haste is NOT the golden number, just a suggestion, there is nothing wrong with having below 400 haste, 400 is only the idealized number in which wrath casts no longer benefit.

This...sorta

Use IDS and Eye and switch some hit gems in and enchant your gloves for precision.

Try to get the Malygos 25 necklace (kill quest), it's still one of the best in the game. It'd have been more practical to have the Sash of Ancient Power too instead of the Leather belt. Hit on trinkets is a good way to get capped fast, but there are usually much better options out there (IoDS and EoB being 2 of them).

Also as Degrador said, spellpower is more important than both haste and crit, so never drop some to try to reach a certain point in haste or crit. It's just not as efficient.

Currently you are at 291 hit, and you want to be at 263, my recommendation would be:

1. Use Dying curse instead of the Stone bringing you down to 254 hit.
2. Replace the Runed Scarlet Ruby in your Crafted Belt with a Veiled Monarch Topaz. This gets you the 5 spellpower socket bonus and brings you to 262 hit.