Something which everyone seems to be forgetting is that mobile artillery is available for this mission too. Here's the strategy which takes care of airborne opposition completely, and you DON'T have to spend all your time worrying about the speeders.....
Take a unit of 6 PTs, 6 AAs, 4 STs, and 4-6 Mobile Artillery units.......Use the PTs & STs to mop up ground forces at the base of the ramp (you can even deploy yr artillery if you want), then undeploy the artillery if you have it set up, and head up the ramp under AA cover...Set your AA's to 1, your PTs/STs to 2, and your MA to 3, then just have groups 2 & 3 follow group 1 (shift/rightclick on one of the AAs with 2 or 3 selected). When you get up by the rebel airbase, set up your artillery, & order them to pound on the base.....Meanwhile, your AAs will pound on any speeders in the area, and your PTs & STs can head up to the top unmolested. Once you've got the rebels cleared from the area, send up your transport w/ Dellis, and take the drill.....Once that airbase is dead, you can use the artillery to also pound on all the rebel structures below the ramp, and shorten your mission considerably.
This is a strategy which I designed after beating the mission twice, and learning that the mobile artillery is one of the most overlooked units in the game, but also one of the most versatile....Definately worth using on this mission, esp since it lets you turn off the Airspeeder tap that the rebel scum is using.
"If there's a bright center to the universe, I'm on the planet its farthest from...."