It is well known that decreasing the carbon content decreases the transition temperature in ferrite-pearlite steels. This trend is less prevalent in ultrahigh-strength steels if strength is maintained at a constant level by tempering. The effect of carbon content on the fracture toughness transition curves for alloy steels containing 0.28, 0.35, and 0.41% C, with strength maintained at 1175 MPa (170 ksi), is illustrated in Fig. 47. There is little effect in the transition temperature range; however, there is a substantial effect in the upper-shelf region, where microvoid coalescence (ductile rupture) is the fracture mode.

Unfortunatey figure 47 could not be copied and pasted here.

The above extract is relevant if you are operating warmer than -25F where the upper shelf region applies.

Following is a listing for tempered 4130 steel:

             UTS        YS

C     F    MPa  psi  MPa   psi  El  RA  HB

205  400  1627  236  1462  212  10  41  467  
315  600  1496  217  1379  200  11  43  435  
425  800  1282  186  1193  173  13  49  380  
540  1000 1034  150  910   132  17  57  315  
650  1200  814  118  703   102  22  64  245  

As you can see, the 800F temper will provide the strength level mentioned in the above discussion and therefore will have the upper shelf fracture toughness characteristics mentioned and because it has the lower corbon content discussed will be the toughest of this variety of ultra-high strength alloy steels.

If you use a factor of .55 x uts for a conservative shear strength, you will have .55(185,000)(.313x.313x3.14/4)= 7,825 with no factor of safety allowed.  If you have the torque applied and the radius to the pin, you know what to do.

If this is not strong enough, you could temper as low as 400F if you can tolerate the lower toughness which is not terribly much lower if you consider that one measure of toughness is the area under the stress-strain curve.

On second thought -- actually it was my first thought but did not think it "through" from the toughness standpoint.

A standard hardened steel dowell pin has very high shear strength as that is their primary function.  Part of that strength comes from the case hardened surface but they have a very tough through hardened alloy steel core.

This will be much much more cost effective and I doubt you will find anything better unless you go to something exotic like carburized 9310 or maraging steel both of which have good portions of Ni for toughness.

We changed from a failing doubled  spring pins to a Driv-Lok Type E with no problems.  We also used their High Shear grooved pins in some tough applications.   

http://www.driv-lok.com/Grooved%20Pins.htm