The value difference between 1OA & 4OA is ~44.7 point in value according to the pick value table on Puckpedia. That point value is equal to the #6OA pick.
Draft pick value charts work better for the NFL than the NHL. With hockey it really does come down to the year.
4OA and spare parts doesnt get you 1OA
It depends on what the Islanders' intentions are. I think there's a misconception that if a team offers up enough draft pick value then the other team would say yes. Typically teams trading down are doing so because they can still land their intended target while adding a couple assets. With regards to Utah, it would depend on whether San Jose or Chicago wanted to move up for Schaefer as well.
The handful of times we've seen a top 2 pick moved:
1993: San Jose traded #2 to Hartford for #6, #45, #58, Sergei Makarov - For better or worse the Sharks decided to take Viktor Kozlov instead of Chris Pronger because they wanted a franchise center.
1998: San Jose traded #2 and #85 to Nashville for #3 and #29 - San Jose had drafted Patrick Marleau the previous year so they thought David Legwand was a redundant piece / they wanted a cornerstone D. Meanwhile Nashville was in its first draft and wanted a presumed high scoring forward to be the face of the franchise.
1999: Tampa Bay traded #1 to Vancouver for #4, #75, and #88 - It was a year without a consensus #1. Most figured Tampa was going to get a winger for Vinny Lecavalier so they'd be debating between Daniel Sedin or Pavel Brendl. After the fact, Tampa GM Rick Dudley said they would have taken Brendl had they kept the pick. Dudley waited to see if Brian Burke would improve his meager offer. Simultaneously Dudley shopped the pick outright and worked out a deal with the Rangers who also wanted Brendl. The morning of the draft, Dudley agreed to Vancouver's offer since he was now a middle man to deliver Brendl to the Rangers.
2003: Florida traded #1 and #73 to Pittsburgh for #3, #55, and Mikael Samuelsson - Florida won the lottery and had Nathan Horton atop their list. Dudley, now GM in Florida, figured he could trade down a spot or two and still get Horton. He tried to drum up a bidding war between Carolina and Pittsburgh but eventually settled on a forgettable offer from the Penguins.