One nice aspect of the .35 Whelen, is bullets can be made from .30 MI Carbine brass. A slight length trim and you have a tapered RN 300gr. bullet for the .35 Whelen - or trimming further, nay weight you want.

Since the working pressure of many modern rounds is 64,000 to 65,000psi using standard, ie: .06 brass, there is no reason the .35 Whelen cannot be loaded to it's full potential.

As has been noted before, A-Square's proprietary ctg. the ,.338/06(same case) has a SAAMI standard pressure of 65,000PSI - then check out the .270 Winchester - another at 65,000PSI, both having the same case and case taper. The .338/06 has listed data for 250's running 2,650fps. If the .35 Whelen is loaded to the same pressure, it will exceed the .338/06- physics is at work here. Judicious loading can considerably improve the .35 Whelen's ballistic compared to Remington's anemic factory loadings.

The round deserves to be more popular. The Sierra 250gr. BT seems to be a good one, as-is the 225 BT for longer range shooting.
Barnes has 180 and 200gr. "X"-type bullets. The 180's can be driven to 2,965fps at a listed 51,900PSI and the 200's hit 2,800fps at 52,400psi - quite a distance off the usable maximum.