Hi
while the 1155 socket can support faster i5 and i7 you need to check with Dell technical support what is the fastest CPU supported by the BIOS and motherboard
It also depends on which case you have (room for larger heatsink & fan)
see
http://i.dell.com/sites/doccontent/shared-content/data-sheets/en/Documents/Dell_OptiPlex_9010_spec_sheet.pdf
which says
Intel® 3rd generation Core™ i7/i5 Quad Core, i3 Dual Core (Post launch) and Pentium® Dual Core (Post launch);
are you planning on buying a new cpu (which will be hard to find) or a second hand one?
regards
Mike Barnes