Currently evaluating Unraid too (v7.0.0), with a Mac client (macOS 15.2 Sequoia). I see the same problem of write bursts with pauses in-between when writing large files (300MB) using SMB, pause seem to occur between files (halving the normal bandwidth). I switched to NFS, and speed is network max. I tried a Linux client with SMB, speed is max too. So isolated it to the Mac. Then found all kinds of server-side and client-side configuration changes for SMB on Mac, none would fix the issue.
SMB appears to be particularly bad on Mac. FTP is not secure. NFS isn't great either (no user account). That'd be great to have some options that works well with Macs (AFP, SFTP, whatever).