The 305 is an improved version of the 30. Have a look through the FAQ X30 section at the top of the page as a starting point. But a couple of points to keep in mind, you are comparing a $1KUSD detector with an 11" DD coil to a $400USD with a 9" concentric.
Using the 10.5" MF 7.5kHz X-Terra coil would make it a fairer comparo. I've not used a Safari but I will venture a guess that DD versus DD the X-Terra will be a little quicker in seeing targets in trash. With the 305 equipped with the 6" DD HF it will provide a combination that will allow you to re-hunt areas you consider hunted outed with the Safari. And I honestly believe, as many on this forum have found, that the 6" HF DD will surprise you with what it is capable of.
I usually continue to go back and attack areas with different detector/coil combination's. And I know from experience that if I were using a stock coil on any of my main detectors, and then went back with the 6" HF DD on the 305, that the number of newly revealed targets would be an eyeopener. If you hunt for long stretches(hours) on each outing, running the Safari till you get a bit arm weary, then switching over to the 305 with the small coil and covering the same area would be a powerful strategy to maximize your field time plus recovery rate.
HH
BarnacleBill