Doom 3

	Asus P5GDC-V (DDR2) - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Asus P5GDC-V (DDR) - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Intel 915P + DDR - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Intel 915P + DDR2 - Pentium 4 560E, 1GB DDR2, ATI X700 Pro
	VIA K8T800 Pro - Athlon 64 3200+ (754 pin), 1GB DDR, ATI R9800XT

Here we see DDR2 having no affect on Doom 3 performance. In fact using older DDR memory seemed to improve performance by a little.

Warhammer 40,000: Dawn of War

	Asus P5GDC-V (DDR2) - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Asus P5GDC-V (DDR) - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Intel 915P + DDR - Pentium 4 560E, 1GB DDR, ATI X700 Pro
	Intel 915P + DDR2 - Pentium 4 560E, 1GB DDR2, ATI X700 Pro
	VIA K8T800 Pro - Athlon 64 3200+ (754 pin), 1GB DDR, ATI R9800XT

In Warhammer 40K: Dawn of War, we have the P5GDC-V using DDR2 out-pacing DDR configurations by a very large margin. The extra bit of performance was very noticeable.