We already have the perfect hard hitting flying asset for the job. The A-10 Thunderbolt II is more affectionately called the Warthog, because it is so damn ugly. It has been scheduled for decommisioning for years, but everytime we get into a little scrape in a desert, we realize how important it is.
It is a tank killer. Can carry basically any type of bomb including laser guided. Carries hellfire missles which are armor piercing. It is also built around the legendary 30 mm GAU-8/A Avenger Gatling gun, the largest, heaviest and most powerful aircraft cannon in the United States military. This cannon can shoot 3900 rounds a minute and can puncture 3 inches of armor from a quarter of a mile away. The A-10 also has excellent low speed and altitude capability. A squadron of these would make mince meet of any creature.
Ah, the area of my specialty when I served with the USAF
The A-10 would be the best pick, due to the low-speed/altitude capabilities you mentioned, but the F-15E would make a great choice as well. They don't get much use, but gun pods can be placed on the aircraft wing stations, in your choice of calibur, from .30 all the way up to 30mm (not the same as the GAU-8). The Strike Eagle can carry a lot more guided ordinance than the A-10, with an on-board Whizzo to run the works. Engagement distance for stationary ground targets can exceed 50 miles, shorter, I'm sure, for moving targets, but still long.
Also, don't discount the M61 20mm Vulcan. Not as much punch as the GAU-8, but same range, and a much higher rate of fire (6000-7200 rounds per minute, depending on the aircraft it's mounted in).
The AC-130 would be brutaly effective: 2 x 20mm Vulcan, a 40mm Bofors gun, and a 105mm howitzer, all radar directed. Other configurations are extant, but this is the one I'm most familiar with.