I would say May 4th is a safe day. You may get some snow, but I doubt very much. If you are woried about it, take a pair as your camp shoes and try walking half a day in them.
I have done a few hundred miles in running shoes now and prefer them to hiking boots. I have hiked and worked in boots for about 25 years and have most likely done thousands of miles in boots, and I have now seen the light. I would reccomend getting your pack weight down first. My current pack weight is 27 pounds full for 5 - 6 days, but I did 150 miles of the At this summer in running shoes with a starting weight of 38 pounds.
I have been using my current shoes which are simply Nike Air Pegasus running shoes for about 250-300 miles of hiking, including all the AT and some of the blue blazez south of Wesser, N.C. So far, besides having some mud stains and a couple of rock scuffs, they are doing very well. Since we need to mention weight, they weigh in at 24.7 ounces for a size 9 1/2 men’s. I honestly haven’t missed the waffel stomper vibram soles because I found my running shoes picked up less mud than any pair of boots I ever used except Army Jungle boots.
For colder weather I have a pair of Seal Skinz socks that I wear over a pair of sock liners. Works very well, as well as my $200 Asolo Gortex boots that now gather dust.
As a converted boot hiker with WEAK ankles, I have actually had less ankle turns and foot injuries since switching to running shoes than I ever did with any boots except the Asolo boots. But the Asolo boots had a very stiff shank on them wich after 10 miles would make my feet numb from the constant pounding they send to your feet. Sure you can step right on sharp big rocks in them and it won’t bruise your feet, it spreads the shock to the entire foot.
Anyway, take any advise you get on the internet and try it for yourself. What works for someone may not work for another. Do a couple of practice hikes before May and see how your feet feel in 2.5 pound boots or 1.5 pound running shoes before you take off from Springer.
SGT Rock