So currently reindexing is at around 51%
(first 40% were without HDD activity, but from there on its constantly 99% usage, is that how its supposed to be?)
That's normal because that is IBD, or we call it Initial Block Download during syncing; it uses high HDD usage; that is why we recommend using SSD if you want to speed the syncing process. There is a significant speed improvement; increasing dbcache will improve the syncing process slightly, but SSD will improve the overall performance of your PC as well as the syncing process.