4.2k attk is nothing. Been boosted to as high as 5.4k before with a +7 and +12 weapon. 40 sin is extremely misunderstood, basically noone knows its strengths and weaknesses (I basically never see people taking advantage of what a sin can legitametely do in 40) (i'm not ever gonna fully go into depth on this because I'd like to still be able to join 40 pvp
). If they did 40 arena would start turning into 50 arena, because 40 sin is so opd that it is similar to how opd a 50 ranger is to 50 pvp. Your the only class in 40 that is capable of criting the xtal for 30k!, one comboing all classes, getting over 150 evade, over 30 crit rate AND maxed crit damage. @ above poster survivability isn't a big deal if you shred everyone in one combo. You can get around 110 evade max non buffed on ambush set fyi, tho around 100-105 is better, since 110 doesn't allow for additional hp/hit/crit/critdmg. But you can also get over 80 evade non buffed on pvp set/windtracker. Windtracker should be best for overall dps, pvp set has the max dps potential, and either pvp or ambush is best for survivability tho its debatable until tested.
@ above poster there is a ton of flexibility in 40 sin builds, all the sets available lvl 30 up are wicked good and can be made opd. It just depends on if you build the sets to their strengths and what your playstyle is. Honestly I would get them all and enjoy them, see how you like them and than decide which you want to improve upon, if say you find yourself using and performing better in one certain set or if you just like one certain set more. Personally, I always found similar success with both ambush and windtracker when I did 40 (pvp set wasn't out.)
edit: what dasher said is pretty spot on as well xd. In that a good sin doesn't rely on evade. And just because ambush is the highest lvl set doesn't make it the best.