These numbers are not bad to be honest, the T3 50th goes for 2000$ in china from resellers, the T17-40th on the other hand goes for about 1800$ , the latter does about 58 watts a TH.

cost per th

T3  = 40$
T17= 45$

40th*5$ = T17 is 200$ more expensive

assuming power cost is 6 cents per kw:

40TH on the T3 cost  =   3.91 $ / day
40TH on the T17 cost=   3.34 $ /day

a difference of  0.57$ a day , so to ROI that 200$ price difference in gears price we do the following

200/0.57 =  350 days almost a whole year

let's see how it stands against S17-53 th which goes for 3500$ in china, it does 45w per th

cost per th

T3= 40$
S17 =66$

difference in 50th = 1300$
assuming power cost is 6 cents per kw:

50TH on the T3 cost  =  4.89 $ / day
50TH on the S17 cost=   3.23 $ /day

a difference of  1.66$ a day , so to ROI that 1300$ price difference in gears price we do the following

1300/1.66 = 783 days or 26 months !!

Honestly, with the numbers ,it makes every sense to get the T3 50th for 2000$ than getting any other gear from bitmain.

These numbers are based on the average price of "buy now" from Chinese resllers, buying the gears directly from the manufacturer will be a lot of different, but the waiting time will be different too.