Now for the sake of simplicity let's say the top teir at each position consists of the top 5 scorers:
The 5th best TE scored 104 pts. Difference of 35 pts from the top TE to the 5th best.
The 5th best K scored 130 pts. Difference of 25pts from the top scorer.
The 5th best Def scored 156pts. Difference of 84 pts from top.
The 5th best RB scored 246 pts. Difference of 168 pts
The 5th best QB scored 312 pts. Difference of 95 pts.
So you can see from the point differential between the best and the 5th best that it is much more important to go for top teir RBs and QBs than it is TEs and K.
10 times out of 10 I would rather draft a #1 WR or #2RB over that top TE. I will gladly give up that 35 total points and take the 5th best TE in the 6th or 7th round in order to get a better WR, RB, or QB in that same 3rd round position that you plan to take Gates.
Heck just doing the math Gates only got 2 or 3 more points per game average than the 5th best TE. Is that worth sacrificing a potential quality WR, RB, or QB?
I notice you kept the WRs out of this part of your post (comparing #1 to #5 at each position).
The biggest reason in my mind to think about Gates in the 4th round is this.
In my leagues odd scoring, this is not Yahoo, WRs, from 1 to 10 or 1 to 20 were the closest bunched out of ANY position.
For instance in my league's scoring...
QBs from 1 to 10 last year was a difference of 12.2 pts/gm
RBs from 1to 10-18.9 pts/gm (24 pts/gm for 1 to 20)
WRs from 1 to 10-4.9 pts/gm (9.3 pts/gm for 1 to 20)
TEs from 1 to 10-8.5 pts/gm
Ks from 1 to 10-3.1 pts/gm
DSTs from 1 to 10-15.3 pts/gm
So, once you get past the top tier RBs/WRs/QBs, which is most definitely by the late 4th round, I would definitely take the absolute best TE over a WR2 or WR3.
The last couple years WRs have been a dime a dozen, I'll get one I can count on, but after that I may even go TE and DST (if a BAL or CHI is there) before getting my 2nd WR (my league only starts 2).
I plan on going...
RB/WR (depending on 2nd)
QB/RB (depending on 4th)
TE/DST if Gates, Chi, or Bal is there...if they are gone already then I'll go WR