So I found an Aussie premodded xbox with EvoX, made it NTSC and some games have been running faster than others for no good reason...

Runs Good:
Official Splinter Cell PAL
Backup Metal Slug 3 PAL (maybe just cause game is extremely small?)

Runs Decent:
Backup Soul Calibur 2 NTSC (takes a bit longer to load, but GC version was also a bit slow on loading)

Runs Bad:
Backup Sonic Heroes NTSC (music stutters like crazy as does menu, can barely make it in game and voice clips stutter)
Backup Tony Hawk 2X NTSC (Gameplay is fine but takes forever to load to it...)

All discs had little/no scratches, FIFA 07 PAL was already on the HD backup but I deleted it, when I ran it, it ran perfectly.

Is this just a bad Xbox laser? Should I just play off hard drive, and if so is it possible to get the hard drive expanded?

Clear the cache (E:\cache\) and the X, Y and Z partitions.

Yes, it might be a bad laser, and yes, you can upgrade the disk. How you do that depends on how your Xbox is modded.