Thanks guys!

@Raffaele: that's great, didn't know there were more recent rt-kernels for debian. I have a 32bit machine, so I'm going to try this one:
http://packages.debian.org/jessie/linux-image-3.10-2-rt-686-pae

I have an nvidia driver (sigh), I guess it's likely that rt-kernel is not going to like it. I read I could patch some nvidia stuff into the rt-kernel, but that's another story. I'll try this first