It depends on "Slow for what?" answers. I have four of these LGA775 systems running in this house. One is a C2Q in my server -- I made a really unnecessary replacement of an E6600 with a Q6600 a few months ago. The remainder are "business" workstations/desktops supporting a total of three users with Wolfdale C2Ds -- an E8400, an E8600 and an E6700 [the 2010 Wolfdale model -- not the Conroe]. All of them (except the server C2Q) are stock-clocked above 3+ Ghz. One uses an Intel Elm Crest SSD (SATA-III) on an SATA-II port.
When I think that these units all deploy technology from 2007/2008, they DO seem like candidates for the recycling pile. At most, I've squeezed ten years from a PC, but in successive use as desktop followed by file-server.
I'm guessing that these LGA775 boxes are still good for a few more years, or until a motherboard goes south . . .
You and I should get together, or, maybe not. Somehow we'd both manage to come out with more systems than when we started....
Like you, I have several Core2Duo systems 'in service' ranging from an E6300/3GB, an E6600/6GB, an E8500/8GB, an E7200/8GB, and assorted AMD systems of the same vintage. They keep getting 'gifted' to me by work, family, friends that muck up something, or the hard drive goes south, or something similar and they just dump it and get something new.
The thing about Core2Duo systems is that being DDR2 most of them have maxed out ram from my pile of disassembled PCS. So, what might have been a dual core 1GB system when originally built usually has 6 or 8GB of ram now.
I use mine for mostly HTPC duties. My E8500 Wolfdale system was my file server and was doing a great job until I got an unnecessary upgrade to an i5. The HTPC systems run fine on core2 hardware.
My mother is still actually on a dual-core Pentium D 945 system (with 4GB of RAM) on Win7 and it actually handles youtube and CPU intensive websites not terrible. I have a core2duo E7200 system ready to go for her when I have the time to transition the files and accounts. She doesn't complain about her current system so I keep putting it off.