I have found a variety of sources that support the spelling of Bentley over Bently.
Let me begin with the deed of 1624 http://www.wikitree.com/photo.php/4/44/Bentley-2142.jpg . In the left hand margin the spelling appears to me as Bentley. I agree that the spelling that begins on line 12 does look like Bentlye. However, in neither case does the spelling appear as Bently. I found this document online at the Online Catalog at the Library of Virginia, which has the record cataloged at Bentley not Bently (in other documents they do catalog with Bently, but not in the case of this deed)
[[http://lva1.hosted.exlibrisgroup.com/F/VYMG51ERFUT84PT4JNPH3V6UL528713XVYMB1U9Q9HTDMNXLXT-03644?func=full-set-set&set_number=000712&set_entry=000004&format=999]].
The transaction of this deed was also listed as Bentley in http://archive.org/stream/originallistsofp00hottuoft/originallistsofp00hottuoft_djvu.txt
The muster list for the Jacob, which appears to be part of the Jamestown 1624/5 Muster Records indicate that a William Bentlie came over on the Jacob
http://www.virtualjamestown.org/Muster/search.muster.cgi?start_page=0&search_type=basic&database=muster_1624&last=Bentlie&first=&muster=&age-op=&age1=&age2=&month=&year=&date=
The site http://www.packrat-pro.com/ships/jacob.htm also has the Bentlie spelling.
So while the muster list does not support either Bently or Bentley but brings in another possibility.
The Minutes of the Council and General Court of
Colonial Virginia uses Bentley not Bently
"Yt is ordered y' a warrant be fent for M r W" Bentley to Teftifie his knowledg between M r Allington and M r fflinton, to be heere one mondye the ix' h of January now next enfwinge."
https://ia700409.us.archive.org/4/items/minutesofcouncil00virg/minutesofcouncil00virg_djvu.txt
William Bentley was placed on trial for the murder of Thomas Godby (whose land Williams was next to according to the deed). A detailed account of the murder and trial can be found at
http://freepages.genealogy.rootsweb.ancestry.com/~swva/Godbydeath.htm
While I do not have access to the sources this person used, I will note that the name is again spelled Bentley not Bently.
William Bentley was also a member of the House of Burgesses. The two sources I have found list William with the Bentley spelling. I believe both of these cites are to Hening I, 137-139.
http://vagenweb.org/hening/vol01-06.htm
http://www.newrivernotes.com/topical_books_1902_virginia_colonialvirginiaregister.htm
Finally, In Southern Historical Families by Boddie, Appendix V The Bently (Bentley) Family, Boddie uses Bentley except in two places, the title of the appendix and once in the first paragraph of the appendix.
I will also point out that the sources who refer to William Bentley coming over as part of the First Supply in 1608, use the spelling of Bentley. I have not gone into detail on this because one could argue this is not the same William who arrived in 1624. But again there is no indication of the spelling Bently.
The profile for William Bently lists Boddie as a repeated source. Yet the printed out copy of the appendix I have does not support the Bently spelling. The other source is created through the import of paf910.ged , I have no way to know if the GED has good sources or not.
I hope this helps. I am open to what others think. I did not mean to imply that the Bently spelling is wrong. In this case, however, I believe the available evidence supports the Bentley spelling.