Okay, I assume you're doing physical damage claws.
Each claw has a "item base", then it has "affixes" or "modifiers" which add additional bonuses either to the claw or to your overall character.
You can see the list of claws (item bases) here:
http://pathofexile.gamepedia.com/Claws
The possible modifiers or affixes that appear on claws are listed here:
http://pathofexile.gamepedia.com/List_of_claw_modifiers
The item base will define the claw's baseline power: base attack speed, base critical strike, and a range of physical damage. In general, the lower down on the list you go, the stronger they are.
In your case, "Thresher Claw" or "Gouger" would be nice for you if you're level 40, since you won't be able to equip the better claws that require a higher character level.
Let's say you have a "Gouger". It has a physical damage range of 13-46, and a base attack speed of 1.5 (And base crit of 6.3% too which matters but I won't be covering in this post.)
So by itself, with no modifiers, a white gouger would have (13 + 46)/2 * 1.5 = 44.25 base physical dps. (Average damage x Attack Speed.)
Of the modifiers that can possibly appear on the claw, only a few are important for a physical damage claw build.
#1: "adds x to y physical damage"
#2: "(x)% increased physical damage"
#3: "(x-y)% increased attack speed"
(Stuff like accuracy or life leech is helpful, but also appear on gear other than weapons, so it's generally preferred to obtain such modifiers on other gear if you need it.)
#1: Let's say your claw says "adds 5 to 7 physical damage"
This adds to the gouger's physical damage range of 13-46, changing it to 18-53.
So a weapon with this modifier would have (18 + 53)/2 * 1.5 = 53.25 base physical dps, a 20% increase compared to the basic gouger which is pretty nice.
#2: Suppose the claw also has "40% increased physical damage"
This is a multiplier to the physical damage rnage of 18 to 53, changing it to 18*1.4 =25.2 to 53*1.4 = 74.2. Thanks to the rules of algebra, you can factor out the 1.4 to avoid extra multiplication.
So a gouger with BOTH the above modifiers would have (18 + 53)/2 * 1.5 * 1.4 = 74.55 base dps.
#3: Suppose the claw has "10% increased attack speed" as well. This changes the attack speed from 1.5 to 1.65, so a claw with all 3 modifiers would have (18 + 53)/2 * 1.65 * 1.4 = 82 base physical dps, almost double as strong as the original plain gouger.
However, if you had the same mods on a weaker claw "base item", say, a "Cat's Paw",
you would have (15+26)/2 * 1.76 * 1.4 = 50.512 base dps, a much smaller result.
So the power of a claw depends on both its base and its modifiers. If you have a "100% increased physical damage" on a really weak base it won't be as good as weaker modifiers on a much better base. +1 socketed gems generally isn't important for the damage of weapon builds because it's an incredibly small boost in power compared to many other factors.
I do suggest trying out the vendor recipe I mentioned in my previous post if your current weapon(s) aren't close to the best base you can currently use - that is, if you aren't using a thresher claw/gouger, try to find one of those and apply the vendor recipe to the item and see if it's any better than what you currently have. It'll give you an okay modifier on the best base you can use at the moment.
For crit, there are two more useful modifiers:
(x-y)% increased critical strike chance. (important)
(x-y)% to global critical strike modifier. (less important)
When mousing over a claw, PoE actually does most of the calculations for you.
For example, I found this screenshot with an image search engine to use an example (it's actually an insanely strong claw).
The third line from the top "Physical damage 111-248" already takes into account the Imperial claw's base damage, the "adds 19-33 physical damage" modifier and the "144% increased physical damage" modifier.
While the 5th line from the top "Attacks per second: 1.65" already takes into account the imperial claw's base attack speed and the "10% increased attack speed" modifier.
So all you need to do to figure out the weapon's base physical dps is (111 + 248)/2 * 1.65 = 296 dps, which is extremely high. It's unlikely you'll find something this good, but I just needed a screenshot to show you how to save a few steps in calculating the weapon base dps.
Generally, you can eyeball the numbers between two claws you want to compare without actually having to do the calculation. If you hold ALT (or CTRL? I forget) while mousing over a claw in your stash or inventory, it'll automatically show the stats of that claw as well as the claw(s) you have equipped side by side for easier comparison.
On poe.trade, the relevant column when you search for claws is "pDPS". "DPS" also includes elemental damage, and if your build doesn't have much in terms of elemental damage nodes on your passive tree, it won't really help much.
Also, for a weapon you want to use a long time, you should apply blacksmith whetstones to it to add "quality", which goes up to 20%. Quality functions exactly like "x% increased physical damage" and stacks with it.