it is the clean up, after the timber company comes in, removes trees, and deals with stumps/root balls. they will come in fast and quick and be gone, and most likely you will not be satisfied with the end results of what they left.
a SCUT to small.
a CUT gives you enough power / weight abilty to deal with the clean up.
if you were going to mess with cutting down trees and root balls, i would be pushing for a higher HP tractor (high end CUT, and getting into Utility class or larger tractor)
google
land clearing site:tractorbynet.com
then click up on images.
above should give you some descent amount of links to read through along with images. to get an idea of what you will be facing with a timber company.
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beyond gravel driveway, also dealing with dirt trails through property, and needing to deal with ground engagement attachments, from box blade, rear blade, FEL (front end loader), to other. and with 45 acres, taking in account estimated length of driveway and trails. a SCUT tractor to small. you be spending more hours on tractor than there is daylight. a CUT will get it done within a reasonable amount of time.