I went from a TIR3 + vector to a TIR5 (w/o the clip) and, honestly, I didn't find the upgrade to be that significant. The biggest improvement did not come from the increased resolution (I didn't have any issues with smoothness with TIR3) but rather from the wider angled lens of the TIR5 which meant that I had more space to move my head about without losing tracking.
The increase of angle is not that great between the TIR4 to the TIR5 (the big jump in angle comes from the TIR3 -> TIR4) and I probably would have been just as happy going to the TIR4. Is the 50$ premium to the TIR5 worth it? For my purposes and in my subjective opinion, no. But I'm happy with the TIR 5 and I know it will serve me for many years to come.
I play mostly RoF and IL2 '46 on a 25.5" monitor.
I hope that helps.
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Asus P8P67 Pro Rev. 3.0
i5 2500k (OC to 4.3 GHz)
AMD 6970
8 GB DDR3
Win7 home 64 bit
450 GB VelociRaptor
"I wanted verisimilitude on par with the real deal to get the sense of immersion that only the best faked reality can bring." Mike Powell