5W30 seems to be just fine for both he 351 and 460. That's all I ran in both.
There's no much benefit to 10w-anything these days, short of reducing cold-start oil blow-by. It used to be that the wider range, the more susceptible it was to breaking down. But any API rated oil seems to hold up fine for recommended intervals.
That said.... neither motor are real picky. They'll run 10w-40 just fine, unlike the Triton motors which growl and sometimes clatter if you run heavier oil.
Heck, I run Castrol High Mileage 20W-50 in my 351W (1969 block, rebuilt something like 20-25 years ago). The engine is a bit tired, and because it sat unused for a number of years, a number of the seals leak oil so that's why I run the heavier oil.
SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.