Expertise is approximately equal to hit rating when in a purely DPS role, but doesn't cap.

4 expertise rating = 1 expertise = 0.25% less dodge
~16 hit rating = 1% hit, 4 hit rating = 0.25% less miss.

[Gloves of the Searing Grip]
[Gloves of Dexterous Manipulation]

Assuming 2x8 agi gems, it's a difference of:

51-33 = 18 agility
42-66 = 24 AP
18 expertise.

So you gain ~0.8% crit compared to 18 expertise (essentially 1.125% hit, although it rounds down so it's actually 1% iirc). I'd probably take the Searing Grip, but it's a close call.

In this case I would definitely go for [Gloves of the Searing Grip] as well. They may be slightly worse or just equal than [Gloves of Dexterous Manipulation], however there is more to them than just theorycrafted DPS values. Searing Grips give you more survivability with more Sta/AC and they actually smoothen out your DPS cycles by reducing dodges. I think the last part is not given enough value by most people but I doubt I am the only one that messes up Powershifts just because the mob dodged your Rip or proceed to Mangle/Shred just because you realized too late that your Rip from before didn't connect, effectively wasting DPS. So unless we are all robots, this is something worth considering for sure.

It's ~6% dodge and ~12% parry. I'd like to see a setup that isn't stupid that actually has that much expertise - it's just not feasible to get that much as a druid with relatively good gear in other slots, in comparison to Hit which it's pretty easy to get over the cap. You would need 16*6 = 96 expertise rating to get dodge capped. Shapeshifters Signet is 20, Searing Grip is 18, One Hundred Deaths is 25, Shoulderpads of the Stranger are 10, Earthwarden is 24, and the Brooch of Deftness is 21. That's a maximum of 118 expertise rating, taken from the WoWhead list of epics with expertise (new in the burning crusade) that's wearable as a druid. It's a pretty select set of gear, to say the least, and certainly not the setup I'd pick for DPSing, even though I agree with Liar that hit and expertise have a slightly more profound effect on personal DPS compared to that given on spreadsheets (also part of the reason I prefer 4t6 over 2t4).

Yes, Deep Shadow is probably the third best in slot after than Don Alejandro's/One Hundred Deaths (as long as you aren't hit capped).

Monstor-- your post proves that when you have more hit rating, you hit more. It offers no comparison of hit rating to 2t4.

Perhaps you could link the WWS parses so we could see the results of your overall DPS.

Also remember that you don't need to get "lucky" with 2t4 for it to be massively better. If you miss a shred, you only lose 8 energy, not 42. Only finishers lose all their energy when they miss.

Your choices of gear change your hit rating by 31, which would take you from 80 to 111, not 128. Perhaps you're omitting the fact that you have your Stranger shoulders with a DPS enchant on them. The [Shoulderpads of the Stranger] have no hit rating on them (and no expertise until next patch). You could get 2t4 in your claim above without lowering your hit rating simply by putting back on your T4 shoulders and enchanting them for DPS.