Fletch and Carrick ticks all those boxes.
1. Carrick and Fletcher both do very well, especially as a duo.
2. Likewise.
3. Penetrative passes don't equate to through balls or defence splitting passes, that's very simplistic and thus very wrong. Carrick's always been very good at playing the delicate, inviting pass that creates space over a short distance and it's led to him being involved as the second or third assister in a lot of our goals, more in the previous three seasons than this. Fletcher's getting better at playing a creative pass but he's not great at it. Think both have room for improvement here, Fletcher more so.
4. Carrick does this very well, Fletcher does it well. Scholes does it magnificently, better than we'll see from a midfielder in our team for another few years yet(at least), I reckon.
5. Barca's midfield aren't great from range, they're still far and away the best midfielder around, proof enough that that's not what you need in midfield i's just a useful add-on.
Midfield Checklist:
1.A midfield needs to be able win the ball, through intercepting on the floor or aerially.
Carrick and Fletch, and Hargreaves waiting in the wings, we possibly are up there in world football if not the best in this regard due to the depth we have in this aspect of midfield play.
2.A midfield needs to retain posession.
I'm sorry but we are poor here, Chelsea, Arsenal, Barca, Madrid all keep posession better than us. Carrick and Fletch would not as a pairing top any of these sides in retaining posession 'effortlessly'.
3.A midfield needs to be able to create chances, via through balls or long range defence splitting passes.
Awful at this, we rarely create chances from central midfield.. hark back to the day of Scholsey threading through balls and the strikers putting them away, these days we rely on Wayne coming deep and thread balls through and then also expect him to finish his own chances

.
Arsenal consistently create plenty of chances through midfield, Barca of course, Chelsea are also pretty creative with Lampard threading good balls and J.Cole/Deco supplying some creativity too at the tip of the diamond.
Madrid have Kaka/V d Vaart, Alonso.
4.A midfield needs to be able to spread the play.
We are decent at this, Carrick stands out at being able to do this... Ando less so and is erratic. We usually are able to get the ball out wide, so no problems in this regard.
5.A midfield must be able to exert concerted pressure in an opponents half and be dangerous from long range (shoot whenever there is an opening).
Little to no threat at all from long range, none of our midfielders are great shakes at long range shooting. As you've alluded to Brwned its a bonus, likes of Arsenal and Barca don't really score much from long range.. but with the Gunners they have Fabregas devloping this side of his game and Ramsey will soon be capable of striking from long range at a consistent level. Barca may solve this problem by signing Fabregas...
Chelsea have Essien, Ballack, Deco, Lampard .. so they're hardly found wanting in this department.
I think apart from number 1. and 4., we are found wanting in quite a few aspects and the ones i'd label as crucial in an attacking sense.