Getting the same thing on my small dedicated server, including some (hopefully) relevant information.
i5-2500K, 16GB RAM (Tekkit has 8GB RAM, install is on a 5GB RAMDrive) - Running Win Server 2012, although I can reproduce this stutter lag in Server 2003 and an extremely stripped down copy of 7 Pro (Which I'm going to digress and say performs like 15% smoother than Server 2012, I am so switching back soon.)
For what it's worth I'm also using mcpc-plus 1.4.7 r1.1 snap 182, if people (Including myself) are also getting the lag in ssp, I'd say this points to the problem being a specific mod, not the core game itself. I'm upgrading to snap 186 as I'm writing this, doubtful it will change anything, but I like to keep my server running bleeding-edge anyway. Where else do bugreports come from?
As far as I can tell, the lag started when lite's version ticked from 0.5.8 to 0.5.8.1, but I've not bothered to go find out what changed between 0.5.8 and 0.5.8.1 - anyone have a handle on that?
None of my players had noticed any lag in the 2 days I was running 0.5.8 and suddenly everyone had it when I deleted /mods and uploaded my client's mods folder to upgrade it.