RAM writes faster than it reads

I've recently created a RAM-Disk on my MBP17" and tried to check the read/write speeds and everything seemed fine. So i did the same test on my MacPro3,1 and i noticed that my RAM (16GB) writes with about 1800MB/s but it reads only with about 900MB/s. I already did a complette machine reset (nvram/pmu/etc), checked with apple's hardware test, swaped graphics card etc but everything seems fine. Is this normal? And if so, why? Btw, i used both, AJA's and Blackmagic's disk speed test app.