duratracs are snow rated and ive heard that they do well in the snow. Kelly safari TSRs are pinnable for studs and are supposed to do well in the snow as well. FWIW, you should be able to find the kellys cheaper than the duratracs. Goodyear makes Kelly tires, just under a different brand.
I agree with ak_cowboy, I was in the same situation and I chose tires, I straight piped my exhaust a month or so later and have yet to regret the decision I also have the 4.6 with 285s and low compression, it still does fairly well.
I've got a 4.2 with 285's and i've got plenty of power. i burn rubber way to much so you should definitely be fine with a v8.