[The Fifth Horseman]

What are your system specs in the first place?
DosBox is quite heavy on raw CPU power needed, and several of the games you have listed (Abuse, X-Com 3 and Tyrian to be specific) needed quite fast machines, approximately 70 mHz and faster (if I remember right).

Data, I tried running T2K at 10000 cycles and even slightly higher myself. No go, it's still lagging.

You might try a few tricks:
1. Dynamic core in DosBox. This doubles the top limit of cycles your machine can handle, but DosBox itself becomes less stable when doing so.
2. VDMSound. This emulates much smaller portions of old hardware then DosBox and thus runs much faster (my machine ran it with X-Com Apocalypse... the resulting speed was completely normal, while in DosBox with frameskip 1 and maximum cycle setting it still lagged)
3. Bootdisk. There is a DOS bootdisk image for download from Abandonia, you might well try using that. That is, if your computer still has a floppy drive...
4. This is a kind of last resort, really, but... building a dedicated DOS rig is still an option. I did it myself and am quite satisfied with the results. No problems with cycles, nearly no problems with compatiblity too... except it might take a fair amount of work to fine-tune such a machine for DOS gaming.