Has there been a hard fork since then? My (old) client is syncing (slowly) but if there's been a hard fork there's not much point.
If you are using version 0.2, I mean to remember there was a hard fork to transition to 0.3 because the consensus algorithm was changed - however, I'm not sure. Version 0.3 is the last one published by the "original developer" in 2014. Since then, there were no hard forks - only soft forks. So with 0.3.x you should be fine - however, at least with Linux I have sync problems with this client, and with 0.4 and 0.5 this has definitively improved.
Yes. The most recent code is on the "master" branch. (There is an experimental 0.6 version but I think it's far from ready.)
(The hardened checkpoints in this source are very old.)
Thanks for reminding that. I could try to update it, but maybe gjhiggins (our current "main developer") anyway wants to renew it for the next version.
BTW, the client seems to be using a crapload of CPU. Load was past 9 on a four core server (that's more than 200% load). Once I stopped slimcoind it went back down to 2.5 (62.5% load). Is this improved in the newer client source and/or is there a way to limit it to using one core only?
Yep, that is a known problem - staking needs much CPU power. You can set a high reservebalance to disable staking (at least temporarily) if the performance is a problem.