It happens randomly, but does not take very long (within 10 seconds of leaving pits, for example) regardless of the 3D settings. Here's the crash info from Event Log. I realise this may be an issue with SoftTH or the D3D8 to D3D9 wrapper, rather than LFS. There is no crash with 0.6E.
Faulting application name: LFS_6E7.exe, version: 0.0.0.0, time stamp: 0x52813c0c
Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000
Exception code: 0xc0000005
Fault offset: 0x45452134
Faulting process id: 0xdcc
Faulting application start time: 0x01cee2fb6b959fd5
Faulting application path: C:\LFS\LFS_6E7.exe
Faulting module path: unknown
Report Id: ee8298f2-4eee-11e3-b931-00106052c624
Event Name: APPCRASH
Response: Not available
Cab Id: 0
Problem signature:
P1: LFS_6E7.exe
P2: 0.0.0.0
P3: 52813c0c
P4: StackHash_498f
P5: 0.0.0.0
P6: 00000000
P7: c0000005
P8: 45452134
P9:
P10: