I really couldn't tell a difference, to be honest.

I tried them side by side in direct sun light and in my garage...
I think in some color settings/combinations (I tried them all several times) the v4 may be a bit brighter as there are combinations of 8 LEDs, instead of only 4 in the v3.

The v4s aren't bad by any means, expect for my opinion of the inconsisent light pattern (blue/white), and are very bright.
A camera blends the light colors into one nice even color, but your eye will not do that... :-(

Sorry to say, I didn't find a compelling reason to move from my v3s.

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2008 4.8i X5 (2/25/08) 105k:
Titanium Silver/Black; All -HUD; Aero Kit; 22" VS-130 w/Pirellis;
///M Shifter & Fr Brakes; Gauge Rings; Console Pads; Custom Wheel & Mats; Roof Rails
Carbon Fiber: Int Trim, Nav Surround, Grill, Cluster Trim, Shifter & Eyelids
1.2" H&R; LUX AEs; LCI Tails; Rear Fogs; NBT EVO; ESS Tune; Meisterchaft GTC Exhaust