It is XP - wouldn’t be much had for a 4Core. +If anything, that E8400 would operate at higher freq., have better FSB dialogue and better L2Cache/Core ratio… What are was you doing for storage?
3.8GHz is like EZ OC preset on a mid-range board. E8400 can do 4.5GHz+. 500FSB isn’t terribly difficult if you’ve got any of the higher quality boards (P45/X48/790i). In fact OP you can often times find really decent 775 boards online for like $50. I saw an ASUS P5N-T Deluxe (780i but not too low end) for exactly that price earlier today. The venerable EP45 series from Gigabyte are also sometimes down in that $45-$55 price range.
Because of the above, but also because Wolfdale was effectively half of Yorkfield. Those Q/QX9xxx chips are just two Wolfdale dies stuck together, so it makes sense that a 3GHz Wolfdale is not looking too bad compared to a 3.2GHz Yorkfield (outside of tests that actually use 4+ cores). The E8400/8500 and somewhat uncommon E8600 are the best balance for performance, thermals, and overclocking to the moon.
i know the q6600 was a good overclocker and would happily run at 3.6ghz.
the e8400 on the other hand can hit 4ghz+
performance wise its pretty close on lightly threaded gaming.(think starcraft 2) but you would get a bump on some games just for having the extra cores on the q6600.(battle field 3 +10 fps with the same gpu).
if its just a show and tell pc for keepsakes then it wont really matter which you choose although the q66 would be more representative of the core 2 era.
as that was pretty much the high watermark for gamers in cost to performance at the time.