Crossfire vid card? memory compatible

I researched crossfire and knew I needed to get same model card to ensure compatibility.
I just got a x1600 pro pci express 512mb and diidn't remember the one I already had was 256mb (same brand/model)

Anyone know if there would be issues with the difference in memory? I've searched but can only find info regarding model/make compatibility. I wouldn't think it would cause problems...but then again, I've never been accused of being smart.

Any feedback would be appreciated! Oh here's a list of my stuff:

Win Home XP SP2
ATX Motherboard – ECS P965T-A
Intel P965 + ICH8 chip
Intel P4 Dual Core 6600@2.4G
2 pairs Corsair DDR2 XMS2 1Gig (2Gig total)
1ea ATI Radeon - Diamond Viper X1600Pro PCI Express 256MB
1ea ATI Radeon - Diamond Viper X1600Pro PCI Express 512MB
Maxtor STM31608 12AS 100G SATA HD
Pioneer DVD-RW 111D
Toshiba DVD-RW SD-R5372
Power Supply – don’t remember make but it’s a 500 or 525W

Envision H190L 19" LCD Flat Panel Display (Response Time: 8ms, Contrast Ratio: 700:1)

Actually Crossfire does allow you to hook up different brands and models of cards. However, both cards will run at the slower speed/specifications. So, essentially your 512MB card will run at 256MB, which to me, seems like a waste of money. I would either upgrade the 256 one, or return the 512 one for a 256 one. Unless of course, you're planning to upgrade in the future, then keep the 512 for now.