You cannot slot Winter's Gift in Swift. Winter's Gift is a Universal Travel Enhancement set, and Swift cannot slot that set (or any other, for that matter).
The "best" way to increase your movement speed while Rooted is to find Enhancement sets that you can slot that will up your running speed in the set bonuses.
Aegis (Resist Damage set) two-piece bonus is a 5% run speed boost.
Regenerative Tissue (Healing set) two-piece bonus is a 4% run speed boost.
And then, of course, there's Gift of the Ancients +7.5% run speed/Defense which always seems to be a popular choice with Stone Armor tankers.
DUH, I knew that I really need to wake up this morning. 
I do have the Gift of the Ancients 7.5% one and a couple of sets that give run set bonuses. I guess the only way I could use Winter's Gift is to keep my super speed and three slot it to get the 6% bonus. Thanks for the help.
No problem. I think everyone has made mistakes like that before. I know I have. (Thinking I could slot Universal Travel powers in Swift, thinking I could drop Jab when I respec'd, all kinds of "whoops, yeah, I knew that" stuff.)
Okay I have a stone tanker and am always on the lookout for a way to up my speed especially when in granite armor with rooted running (I think I may slightly slower there than if hit by a slow affect).
Is there any "good" way to use the winter gift enhancements to up my speed decently all the time? The only place I can think of using them is in swift but I am not sure how much that will really get me. Note: I am not talking about the 6% bonus for all three just the % increases from the two enhancements with run speed increase.
Thanks,
Gray