The very, very top gear comes from the last boss in Naxx25 (ilevel 226) and Malygos25 (ilevel 226). Naxx10 drops ilevel 200 gear, except KT who drops 213. Naxx25 drops ilevel 213 gear, except KT who drops 226. The differences are fairly minor -- for example the difference between T7 and T7.5 gloves is like 10 spell power, a bit more stam/int, and slightly more hit/crit -- nothing insane. Heroic end wing bosses also drop by the way ilevel 200 epic gear, putting them on the same level as naxx10 gear (also much of the crafted gear is iLevel 200).

Anyways its definitable doable I think to solo or dual-play all the bosses in naxx10, it would actually be easier to 4-5 box in Naxx25 however. You are going to wipe a lot, and you are going to need to gear up a bit (esp tanks/healers) in heroics, so you are looking at least a few weeks of running heroics daily in conjunction with weekly naxx/voa/os so you can be geared enough for the latter bosses. You can start on anubrekan, noth, faerlina, patchwerk, grobbulus, and a few others in just blues though.