Based on my experience I am not certain how the most Core 2 Duo processor equipped Macs are going to fair with El Capitan, it was clearly slower than Mavericks (unsurprisingly Snow Leopard is much faster than both of them).
This my experience as well. I ditched El Capitan in favour of Mavericks, a step not taken lightly. El Capitan is better than Yosemite as far as system performance is concerned, at least for me. Snow Leopard is of course unparalleled and I am still not sure why the system performance got so bad with Lion and later. Animations are fluid, the MacBook runs cooler overall, applications start quickly. It is really strange how it got so bad. I can accept that programs will require more CPU and graphics performance, but the problems started with Lion and Yosemite just happened to take the flak more recently. Newer hardware can mask these problems, as older hardware is generally where performance degradation is the most noticeable.