Lipo - 25c 5100 or 30 c 5000 ???

I am having hard time with this simple decision:
I am going to invest some good money in some good pair of Lipo's. I am a basher. I have a stock e-revo and will surly go for a brushless upgrade (c-c 2200kv combo, I believe) sometime soon.

The question:
should I buy these (119$):
Poly RC Professional "XQ" 30C 7.4V - 5000mAh

or these (115$) ?
Poly RC Professional "XP" 25C 7.4V - 5100mAh

Just have heard a rumor that the XQ cannot hold the voltage so good as the XP. Someone knows anything about it ? someone have any experience with one of those ?
please. help needed...