Memory wont run dual channel with same timmings as single channel

I got to sticks of KVR PC-2700 for my little brother's rig and they both look and behave like CH-5. When I tested the sticks individually, they were both memtest stable @ 200fsb & 2-2-3-11 timmings. However when in dual channel, the best timmings I can get are 2.5-2-3-11. What's going on?

My bro's rig:
2100+ AIUHB 0302 MPM @ 11.5x208 =2401mhz (cpu interface enabled)|Abit NF7-s rev2.0 D23 Subzero|1GB KVR PC-2700 |WD1200 JBRTL| Gainward FX5700 256MB | thermalright slk947u with ttsf2|